Developer Needed to Build eBay Sold + Active Listings Data API for Used Auto Parts

We need an experienced developer/data engineer to build a reliable API that returns eBay market data for automotive parts. We already have our own developer. You are not building a frontend or full application. Your responsibility is specifically the market-data/API layer. A request may look like: 2006 Mazda 3 + Climate Control And the API should return structured data such as: ( "query": ( "year": 2006, "make": "Mazda", "model": "3", "part": "Climate Control" ), "active_count": 182, "sold_30_days": 11, "sold_60_days": 24, "sold_90_days": 37, "sell_through_90d": 20.33, "average_sold_price": 64.50, "median_sold_price": 59.99, "minimum_sold_price": 35.00, "maximum_sold_price": 110.00, "average_shipping": 11.25, "sample_size": 37, "last_updated": "2026-08-10" ) Sell-through rate will be calculated as: Sold Quantity ÷ Active Quantity × 100 Example: 37 sold / 182 active = 20.3% sell-through Data Required We ideally need: Current eBay active listing count Sold/completed count for the last 30 days Sold/completed count for the last 60 days Sold/completed count for the last 90 days Sell-through rate Average sold price Median sold price Minimum and maximum sold price Average shipping price when available Sample size Last updated timestamp Example active and sold listing IDs/URLs for verification Automotive Search Accuracy Accuracy is extremely important. A search such as: 2006 Mazda 3 Climate Control should not return a bunch of unrelated HVAC parts, knobs, repair services, manuals, accessories or parts for unrelated vehicles. The system should be able to: Search using Year / Make / Model / Part Use eBay Motors categories where applicable Use vehicle compatibility/fitment data when available Normalize common automotive part names and synonyms Account for different ways sellers describe the same part Default primarily to Used condition Exclude irrelevant listings Exclude repair services, manuals and unrelated accessories Handle pagination properly Remove duplicate results where possible Distinguish number of listings from quantity sold when the source provides that information Data Source You may use: Official eBay APIs Third-party automotive/eBay data APIs A combination of multiple sources Another reliable production-ready solution We care more about accuracy, reliability and scalability than the specific technology used. The most important requirement is having a reliable method of obtaining sold/completed eBay listing data. Please do not accept the project and then discover afterward that your chosen API only provides active listings. API Requirements The completed API should: Return clean JSON Have documented endpoints Be simple for another developer to integrate Include authentication Handle errors properly Handle retries Handle pagination Handle API rate limits Use caching where appropriate Avoid unnecessary duplicate requests Support configurable search periods where possible Include clear developer documentation Be production-ready Be designed to scale Volume / Scalability Please assume the system may eventually perform approximately: 100,000+ searches per month Your proposal should explain: Whether your solution can support this volume API rate limits Third-party data costs Expected cost per 1,000 searches Caching strategy Infrastructure requirements Any practical limitations at scale We do not want a solution that works well for 10 searches but becomes extremely expensive or unreliable at larger volumes. Paid Proof of Concept We want to start with a small paid POC before committing to the full project. We will provide approximately 5-10 Year / Make / Model / Part combinations. For each search, the POC should return: Active listing count 90-day sold count Sell-through rate Average sold price Median sold price Sample active listings Sample sold listings We will manually compare the results against eBay to evaluate accuracy. If the POC performs well, we will move forward with the full API. To Apply Please answer these questions directly: Exactly how will you obtain eBay sold/completed listing data? What API or data source would you use? Can you provide both current active listings and trailing 90-day sold listings? Have you worked with eBay APIs before? Have you worked specifically with eBay Motors? Have you worked with automotive fitment/compatibility data? How would you prevent unrelated listings from affecting the results? How would you handle different names/synonyms for the same automotive part? How would you handle pagination? How would you handle rate limits and caching? What would approximately 100,000 searches per month cost in API/data-provider fees? How quickly can you deliver the POC? What would you charge for the POC? What would you estimate for the completed production API? Please do not send a generic proposal. Start your proposal by explaining exactly how you plan to obtain reliable sold/completed eBay listing data. Experience with eBay Motors, automotive data, vehicle fitment or automotive parts is a major plus