After doing some research, it's either:

Avicularia diversipes
" " minatrix
Other unknown species

A. diversipes looks closer to yours though

Get the big breeders name, if the seller will give it to you and approach him and ask him if he has been selling this species of Avic.

How much did you pay for it?
Cause you can buy an Avic avic for cheap price now a days.

It is a gamble, as you said.

For the price you paid i would return it, as A.avic (Guyana) slings are going for R160

If you did not pay a ridiculous amount for it I would keep it to see what it turns out to be. At that stage though it could be anything....I own 7 different species of Avics and at sling stage the majority of them look quite the same. A few exception of course (A.minatrix,diversipes, purpurea, versi,etc) are easier to identify. But yours is definitely not one of those.

It's definitely an avic, but I would rule out dicersipes as well. Diversipes is much more metallic with different colours. I agree with Zane, depending what you payed for it I would keep it and see what it turns out to be. If it is a avicularia sp "green yuyana" or metallic green or something it would be a special one to have, they're pretty hard to find and go by different names.

If you want a guaranteed green Avicularia then get a sp. metallica green or sp. Kwitara river (probably one in the same anyway). Avicularia sp. Guyana/avicularia/whatever they are being labelled up as these days have very variable colouring ranging from fairly light blue through to green and they can even change colour from one moult to the next (see here ).