1) Use their advanced search settings like a boss.
2) Change the "sort" function.
The default sort function on eBay is set to "Best match" which uses an algorithm to sort results according to what's relevant, how popular an item is, when the auction time for items end and a seller's track record. Change the sort button to suit your needs the most. If saving money is your priority, go for "Price + P&P: lowest first" to yield results with the lowest product price as well as lowest packaging and postage price (P&P).
Following enables your eBay feed with relevant content whenever you log in. If you're looking through eBay for a particular product, but can't seem to find an exact match, you can decide to "follow (this) search" to set up your eBay newsfeed and can also take it a step further by ticking on "email me new items that match this interest" in order to be sent email notifications whenever new items under the same category are listed.
4) Making deliberate spelling mistakes can help.
It's strange, but how many times have you incorrectly spelt something only to get back an interesting result that wouldn't have appeared in the first place without the typo? Likewise, sellers are only human and they can make all sorts of typos that eBay will not correct on their behalf. So if you're looking for a Givenchy product, but can not find what you want under "Givenchy" (the correct spelling), try "Givency" instead- you never know!
5) Include description.
A lot of people think that search engines will return results that include what you put in search from the descriptions of the items themself, but this is not necessarily true. You have to enable the "include description" box right beneath the "search" button in order to expand your search to an item's description too.