So I’m trying to sell tee shirts on my wordpress, and using the donate email link doesn’t work because there’s no way for my clients to tell me the size and color they want. Any ideas on how to solve this problem?
WordPress.com blogs aren’t intended for ecommerce. Even though the blog appears to be a nonprofit blog and the sales might be conceivably considered “donations,” you might still be in violation of the ToS.
If you are actually making the shirts yourself, you can sell them through etsy — which does not allow reselling — and then link to your etsy store.
Basically, if you want an ecommerce site, you need to self-host with wordpress.org software or seek another solution on a different blogging platform.
Perhaps someone else has a more hopeful answer for you, but I think you’ll need to think of a different venue for marketing your shirts.
Custom form code is not allowed at WordPress.com, and so you cannot use the PayPal custom size and color form options you mentioned. If you would like more control to customize and to add e-commerce options like that, mmadfan is correct that you need to look into using WordPress.org instead. See http://en.support.wordpress.com/com-vs-org/ for more details.