I think this question belongs
here.
Although it is not about an individual trade, you can get the help you need on this thread ^^
What I can input to answer you question is, like smoothiemaster said, it would depend on the rares you are auctioning and what rares/very rares you would want in return, but I can tell you that no 8 rares on the site would be fair for any OMG so rare pet.