To find the right deal and ensure the item is legitimate, look in the appropriate category (whether it be Health & Beauty, Music .. whatever it is you're looking for, look in the category). If you have already selected a more specific category you're after (e.g. Fragrances, Make Up etc.), great! However, it is worth noting that some items may not be in the specific category (such as Fragrances) but rather in the collective category (such as Health & Beauty).
If you have found an item but unsure whether it is legitimate, perhaps you should look at the top-right of the screen where it states the percentage of positive feedback. This is the key to locating a great, legitimate deal many overlook (or simply do not spot). Sure, some people may be lucky and get the 'real deal' (as David Dickinson would say) every time but don't try your luck, just use your common sense and be sure that you're not wasting your money.
If you are unable to locate the item on Ebay or you cannot buy it, you may just have to wait until someone else sells it to which you can strike ... or maybe you will just have to save up if the bids (there are more than one of your intended item) do not expire by then. That leads me on to something else, Bidding vs Buy It Now.
Both are very efficient, both require money (PayPal is the way to go may I add, it's safer). I do, personally, prefer Buy It Now because you do not have the hassle of having to increase your bid when you're outbidded, you can just be sure that the price will be the same. If you're a fan of auctions and like competition then go for it, but don't expect anyone else to help when your planned expenditure is much more than you had hoped. Having said that, Buy It Now tends to be of a high price initially (particularly with electronics) and bidding tends to start low but then work its way up. It is your choice whether you want to have a fixed bid or an ever-changing bid.
Happy buying ... I hope