There seems to be an error in Barry's advice for excluding eBay from a Google search. The minus sign needs to be immediately in front of the excluded term (without any gap) but there most definitely should be a gap in front of it.
Returning to the main them of your question though, Woodelf, while eBay was originally set up as an auction site, over 90% of items sold on it these days are sold on a 'Buy it Now' basis. If, after making an initial search, you select the filter in the left-hand column to only show 'But it Now' offers, you're left with a site which works in exactly the same way as Amazon does and is therefore quite easy to order from. (It's only if you're interested in bidding for auctioned goods that things start to get a bit trickier).
So, for the vast majority of stuff that you might be seeking, the 'Buy it Now' filter will be the key that unlocks eBay's functionality for you.