Yes we do offer Ebay Repricing. Its not as easy as using ebays API to find all the sellers of a particular item. If you look at the ebay api, it actually states that the ebay api does not contain all items that you can find on ebay.com and it also does not always have live data. So without live data and without all the data your really at a loss. This is on top of the issue around eBay not being a catalogue driven marketplace.
In general you can trust the search from eBay to be the same as on the site. There are very few exceptions that we've found over the years and most of them turn out to be bugs or eBay being slow to reindex. There is one notable exception to this dealing with Half.com listings which I first reported to eBay over 4 years ago.
eBay is absolutely more difficult than Amazon. When Price Spectre first launched in 2009 the eBay catalog was extremely limited. Even from 2010 - 2011 eBay claimed only 30% of products on the site fit in the catalog. I'm not sure what the number is now but it is still relatively small. eBay will never be fully cataloged and can't be. A good example of why would be someone bundling products together that didn't come that way from the manufacturer. What we've found is that sites outside of the US have an even weaker catalog. This makes a repricer like Price Spectre even more useful on those sites.
Repricers that support eBay tend to only work with listings in the catalog so have limited functionality if you need eBay pricing data. With very few exceptions Price Spectre can dynamically reprice almost any listing on eBay based on competitor prices by allowing the seller to specify search keywords. The majority of our business has always been non-cataloged keyword searches and that is reflected by eBay's weak catalog.