Yixing is a whole subject of study in itself, as those of you that are into it aptly show us :) There are a lot of things to consider, especially in the clay, that seem a bit esoteric to the beginner. I know there are a lot of poor pots out there with awful clay that could probably ruin a tea. Since many of us in the states don't have the ability to go to different stores and talk to someone knowledgeable, we have to buy most of our pots online. I am personally lucky enough to have a local vendor that I trust who is pretty knowledgeable and sells pots with good value, but many people here are not.
So I think that it would be really valuable if some of the more knowledgeable members here could give some basic tips on things to look for when choosing a pot - especially (but not exclusively) online. Note that I'm talking about pragmatic qualities, and not qualities that would only affect collector's value. Obviously there's only so much you can find out online, so buying online will always be a gamble to some extent, but what can a beginner look for to raise the chances of getting a good pot?
One thing I would also like to see, and I think it would be appropriate here but may warrant its own thread, is an abbreviated list of clay types and their properties. For example: "Duanni: white clay [other visible properties]. Highly porous, tends to absorb more than others like x, y, z. Often better for non-fragrant teas or teas with deeper bass notes like a, b, c."
I know that many of these things are covered in some depth in other threads here and on TeaChat, but I think that the key there is that it's in depth (even if it's not terribly deep). What I would really like to see is something akin to a reference sheet that a beginner could keep in mind when looking for a pot. I think that a good list of things to avoid would also be quite valuable here.
Some things that I have picked up myself over the last couple years:
- Find a trustworthy vendor
- Look for tight clay, which should have a sort of satin finish (not waxy)
- Stay away from anything that looks like it has tea stains, especially when they're cheap, unless you can really trust the vendor. You're not going to get an antique for a low price and there are many out there rubbed with shoe polish. (Since some seem to actually not mind this, I think it's worth keeping in mind that shoe polish contains added oils meant to nourish leather that surely get absorbed by the teapot and probably won't come out except in your tea.)
I could probably come up with more, but it's late and I'll leave it to the experts. I could be wrong in my few tips, too, but it should at least give you an idea of what I'm thinking.