Auction Site Buyer Premium Highlighter

WHAT IT DOES

This userscript helps auction bidders understand the true cost of winning an item by revealing the buyer's premium and other hidden fees. It scans auction listing pages—eBay, live auction sites, GunBroker, Bonanza, and similar platforms—for buyer's premium percentages and additional charges not included in the bid price. It then displays a calculator showing the total cost including premium, the premium amount, and the effective percentage increase. If you set a budget limit, the script highlights whether the total cost exceeds your budget and suggests a maximum bid amount to keep the final total within your limit. It also warns you if the premium is above a configurable threshold (e.g., 15%) with a red warning badge.

WHERE IT RUNS

The script works on auction and bidding site pages—eBay, live auction platforms, GunBroker, Bonanza, and similar sites. It runs entirely within your browser, reading only the visible content of the current page. It does not track your browsing history, access other tabs, or send any data externally. All calculations are performed locally.

HOW TO USE

After installation, open the panel by clicking the tool's icon in the BotGentz sidebar. The script auto-scans auction pages on load (toggle this on/off). Set your budget limit in the settings to see if the total cost fits your budget. Choose your high-premium threshold (10%, 15%, 20%, or 25%)—premiums above this threshold will be highlighted with a warning. Click "Scan for premium" to manually analyze the page. The panel displays the buyer's premium percentage, total cost including premium, and whether it stays within your budget. If the current price isn't available, you can enter your bid amount manually to calculate the total cost. Use "Clear calculator" to remove the display.

THE TECHNICAL MECHANISM

This script uses pattern matching to detect buyer's premium percentages from page text. It scans for patterns like "buyer's premium 15%", "premium: 12%", "15% buyer's premium", and "hammer price + 10%". It also searches premium-specific elements using selectors like .premium, .buyer-premium, .buyers-premium, and [class*="premium"]. If no premium is found in dedicated elements, it scans the entire page text. The current price is extracted using regex patterns and common price selectors. The script calculates the total cost as bid price × (1 + premium/100). If a budget is set, it calculates the maximum bid that keeps the total within budget: maxBid = budget / (1 + premium/100). Premiums above the threshold are highlighted with a red color and warning badge. If multiple premiums are detected, the first one is used.

THE PANEL

The panel is draggable anywhere on the screen and remembers its position between sessions. It can be collapsed to a small floating bubble to minimize distraction, and expanded again with a single click. The panel's width can be adjusted, and pressing the Escape key closes it instantly. All settings—display mode, budget limit, high-premium threshold, and auto-scan—are persisted locally using GM_setValue, so your preferences remain intact across page reloads and browser restarts.

PLEASE NOTE

This userscript requires the free BotGentz extension to function. The script is designed for auction and bidding sites; it may work on other sites with similar fee structures but is not guaranteed. The buyer's premium detection relies on the current text patterns on each site—if a site updates its UI or wording, the script may need to be updated. Some auctions may have additional fees (shipping, handling, taxes) not included in this calculation. The budget suggestion is based on the buyer's premium only and does not include other costs. Always read the full terms and conditions before bidding. The script does not access your account or API; it only reads what is visible on the page. No data from your browsing is stored or transmitted anywhere—all processing occurs entirely in your browser.