hmmm I dunno how you'd tell a fake fake tan tbh! Maybe if you're going to go for an expensive brand have a look on some of those cheaper pharmacy websites or amazon as well as ebay? I bought mine on a bit of a whim really but happy with it. Smells so lovely as opposed to the Johnsons or dove ones which smell a bit like potatoes. But if you apply it at night it might not matter.
I found that Dove and Johnsons took ages to build up and were difficult to get even . I tried that st moriz stuff from semi chem , v cheap but iv tried fake bake and gosh and you cant tell the difference .
Ok I'm sorry but I live in fake tan all year round (I think tanned fat looks better than white fat).
My favourite build up moisturising tan is Garnier Skin Naturals. It builds up quickley and has a nice apricot smell to it.
My favourite fake tan is a st tropez fake called st moritz. Its £2.99 from t j hughes, savers, bodycare/grahams. Its a mousse that you apply with a mit. Its already brown so you can see where you're putting it and where you've missed and then it gets browner over a few hours. It says on the bottle apply it after you've showered in the morning and let it develop all day but I actually apply it at night after my bath, it takes about 10mins to dry and then I go to bed with it on and shower it off in the morning. Many people then ask if I've been away if they haven't seen me or a while