Hi all, I'd just like to reinforce everything JoAnn has said. A low fired pot can have pretty colours you can't get at stoneware temps, like pink for example, but it will also craze, absorb water, and could therefore crack overnight for example in Canberra. Can still be a good pot if you don't let it freeze. It's cheaper to fire to lower temperatures, but not acceptable for dinnerware for example. Sometimes I make pots in a fine white earthenware; pretty glazes, but I label them clearly so the potential customer knows they are not safe in a hard frost.
It's normal among potters, if one is not sure which clay a fired pot was made with (meaning earthenware or stoneware) to touch one's tongue to it somewhere to check how absorbent it is. I was taught this in pottery classes. Very absorbent, ie 'grabs' your tongue, means earthenware.
I once (before I learnt to pot) bought a vase in a market, from the potter, not 'trash n treasure'. Got home, put water and flowers in it, placed it on the mantlepiece - I think the ring made by the water gradually seeping through is still there! I felt very cheated, and only placed dried grasses in it after that.
Most of the bonsai pots I make now are stoneware, especially since I got the gas kiln. My ancient electric kiln really struggles to get to the temps for stoneware. But I recently made myself some earthenware pots with glazes I hope will look good with my maples in autumn. I chose the earthenware for these for the glaze colours I could have, and because I haven't seen a frost where I live for over 20 years, and the frosts I recall from way back were unlikely to be hard enough to crack pots. So I figure I'm safe. And if they deteriorate, I can just make myself some more, can't I?
Other things to consider are whether the pot looks neat, well finished. (Some of mine don't, but if I sell those I offer them cheaply, as 'seconds'. And they are snapped up.) Check for rough edges where there shouldn't be, check how well the feet match each other, check there are holes to wire the tree down as well as suitable drainage holes.
If you are thinking of making your own, by all means do so, but don't expect instant success or that it's cheaper. And pottery teachers are (mostly) used to pots having flat bases to sit on for firing - pots often warp in the firing when sitting on their feet. At least they do for me! If you don't buy a kiln, paying firing fees usually makes your pot dearer than you'd have expected, and you still pay in full if the pot broke or exploded in firing. But it can be a wonderful and rewarding activity, when it goes well.
Like JoAnn, I don't usually make to order. It raises the stress level, and often has an unhappy ending. I want to have fun.