What's the most amount you've sold on Cardcash in one go?

I have quite a bit of gift cards that I feel I should just sell at this point instead of keeping for years. Is there a limit to how much you can sell to them? Is there a risk at selling too many on one go? I wouldn't do a lot if I had to send them in since it could get lost in the mail, but the ones that don't require sending the cards in.