How good in quality do fullart Pokemon cards have to be because I'm looking to sell mine and I have a base2 Sandshrew

You're gonna have to go there and ask them if they'll buy them. Quality is a huge factor and only the buyer can determine if they actually want the cards upon seeing them for themselves. That being said, Base Set 2 Sandshrew is worth like 20 cents.

With mtg cards anyway, mods don't mean much if anything for value, so i wouldn't expect anything more than the card itself sells for for moded cards.