How to Use Competitor Out-of-Stock Data to Optimize Ad Spend

In high-stakes e-commerce, the most expensive mistake you can make is playing a fair game. When bidding on high-intent keywords like "Sony 65-inch 4K TV," you aren't just competing on product quality; you are competing on wallet depth against retail giants like Amazon, Best Buy, and Walmart. A static "always-on" bidding strategy often leads to overpaying for clicks in a saturated market.

There is a recurring moment of extreme vulnerability for even the largest retailers: the out-of-stock (OOS) event. When a competitor sells out of a trending item, their ad spend often continues to flow for hours before their systems catch up. Sometimes they suddenly go dark, leaving a vacuum in search results.

You can turn this into a strategic advantage. By monitoring competitor inventory in near real-time, you can programmatically surge your ad spend the moment a competitor hits "Sold Out." This guide explains how to build an inventory-aware bidding engine that captures stranded demand and maximizes ROAS.

The Strategy: Arbitrage on Availability

Most performance marketing is reactive. We wait for a platform’s algorithm to decide if a click is valuable. Inventory-triggered bidding is proactive. It uses external market signals to determine value before the auction begins.

There are three primary tactics to deploy using competitor inventory data:

• The Surge: When your primary competitor goes OOS on a specific SKU, you increase your bid modifiers (e.g., +50%) for that product's keywords. Since the user can't buy it from the "big guy," your conversion rate naturally spikes, justifying the higher cost-per-click (CPC).
• Conquesting: If a competitor is out of stock, it is the perfect time to bid on their brand name keywords (e.g., "BestBuy Sony X90L"). You are offering a solution to a frustrated shopper who just saw an "Add to Cart" button disappear.
• The Pause: This is an internal defense. If your own site goes out of stock, you should stop the ad immediately. While Google Merchant Center eventually catches this, a custom scraper can detect OOS status and pause ads hours faster, saving thousands in wasted clicks.

Shifting to an inventory-triggered approach also improves your Quality Score. Sending users to a page where they can actually complete a purchase reduces bounce rates and signals to ad platforms that your landing page is highly relevant.

Identifying the Signal

To automate this, you need structured data. You aren't just looking for a price; you need the availability signal. When you scrape a competitor's product page or category list, you must map their data to yours.

Most major retailers use specific strings or CSS classes to denote stock status. Extract these into a normalized format. A typical JSON output from a competitor scrape looks like this:

{
  "timestamp": "2023-10-27T14:30:00Z",
  "competitor_name": "BigBoxRetail",
  "product_name": "Sony - 65\" Class BRAVIA XR X90L LED 4K UHD Smart Google TV",
  "sku": "6544733",
  "internal_mapping_id": "SNY-65-X90L",
  "price": 1099.99,
  "availability": "sold_out",
  "shipping_status": "unavailable",
  "inventory_level": 0
}

The internal_mapping_id is the most critical field. It allows the bidding script to recognize that "6544733" on the competitor's site is the exact same product as "SNY-65-X90L" in your warehouse.

Mapping the Landscape

Scraping individual product pages is inefficient if you carry thousands of items. Instead, use category scrapes. By targeting category URLs, such as "All Gaming Laptops," you can grab the stock status of 50–100 items in a single request.

A reliable monitoring workflow follows this logic:

1. Input: A list of competitor category URLs.
2. Extraction: A scraper identifies each product card and extracts the SKU and stock status.
3. Storage: Data is pushed to a centralized database or a Google Sheet.
4. Trigger: An ad script reads the data and adjusts bids.

Overcoming Proxy Blocks

Major retailers like Best Buy or Amazon use sophisticated anti-scraping measures. Attempting to check stock levels every hour from a single IP will result in an instant block. Use residential proxies to succeed. These allow the scraper to appear as a regular shopper browsing from a home connection, ensuring you see the live stock status rather than a CAPTCHA.

Connecting Data to Decisions

Once the data is in a Google Sheet or database, you need to define how the ad platform should react. Google Ads Scripts are the most accessible tool for this, allowing you to write small amounts of JavaScript that interact directly with your campaigns.

The logic for an inventory-aware bidding script looks like this:

# Logic for an inventory-aware bidding script
for product in our_inventory:
    competitor_status = get_competitor_status(product.sku)

    if product.in_stock and competitor_status == "OUT_OF_STOCK":
        # Competitor is vulnerable
        set_bid_modifier(product.keyword, increase_by="50%")

    elif not product.in_stock:
        # We are vulnerable, stop wasting money
        pause_ad_group(product.id)

    else:
        # Business as usual
        reset_bid_modifier(product.keyword)

Implementation with Google Ads Scripts

You can set a Google Ads Script to run every hour. It fetches the latest scrape results from a URL and applies changes. This functional snippet provides a starting point:

function main() {
  // URL of your scraped data (e.g., a published Google Sheet CSV)
  const DATA_URL = "https://docs.google.com/spreadsheets/d/your-id/export?format=csv";
  const response = UrlFetchApp.fetch(DATA_URL);
  const data = Utilities.parseCsv(response.getContentText());

  // Iterate through the rows (skipping header)
  for (let i = 1; i < data.length; i++) {
    let [internalSku, competitorStatus] = data[i];

    // Find the ad group associated with this SKU
    let adGroupIterator = AdsApp.adGroups()
      .withCondition(`Name CONTAINS '${internalSku}'`)
      .get();

    if (adGroupIterator.hasNext()) {
      let adGroup = adGroupIterator.next();

      if (competitorStatus === "sold_out") {
        // Increase bids by 50% when competitor is OOS
        let keyword = adGroup.keywordTargeting().keywords().get().next();
        keyword.setMaxCpc(keyword.getMaxCpc() * 1.5);
        Logger.log(`Surged bids for ${internalSku} due to competitor OOS.`);
      }
    }
  }
}

Internal Defense: Protecting Your Own Budget

While attacking competitors is effective, saving your own wasted spend is often more profitable. Google Merchant Center (GMC) is the standard way Google tracks your inventory, but GMC feeds often update only once every 24 hours.

If you sell out of a hot item at 10:00 AM, you might continue paying for clicks until the following morning. If your average CPC is $2.00 and you get 500 clicks a day, that is $1,000 lost on a single SKU.

By scraping your own site or querying your internal Product Information Management (PIM) system and linking it to the script above, you can pause ads within minutes of a stock-out. This ensures every dollar spent has a real chance of resulting in a conversion.

Pitfalls and Recommended Approaches

Implementing this strategy requires precision. Keep these considerations in mind:

• Frequency vs. Cost: You don't need to scrape every minute. For most industries, a check every 4 to 6 hours is the "sweet spot" between data freshness and proxy costs.
• SKU Mapping Accuracy: Ensure your mapping file is accurate. Increasing bids on a "Sony TV" because a competitor is out of "Sony Headphones" will quickly drain your budget.
• Platform Delays: Ad platforms have a slight lag. Avoid setting scripts to toggle bids too aggressively (e.g., every 15 minutes) to prevent account reviews or spend inconsistencies.

To Wrap Up

Inventory data is a powerful hidden signal in e-commerce. By moving away from static bidding and toward a dynamic, scrape-driven model, you can stop fighting for scraps and start capturing high-intent traffic exactly when your competitors cannot fulfill it.

Key Takeaways:

• Monitor the gaps: Use web scraping to identify when competitors go out of stock on key SKUs.
• Surge aggressively: Increase bids on keywords where you have the availability advantage.
• Automate the bridge: Use Google Ads Scripts or Meta Rules to connect scraped data to your bidding engine.
• Protect your budget: Use the same technology to pause your own ads the moment you sell out.

Start small. Pick your top five best-selling products, monitor your main competitor, and track your ROAS as you capture the traffic they’ve left behind.