Buying a kiln goes wrong in the same four ways, and all of them are avoidable by answering four questions before looking at any listing: what supply is available, where it will stand, how big your work is, and what temperature you fire to.
What supply is available
A standard socket caps you at about three kilowatts and a wide range of small kilns. Anything larger needs a dedicated circuit and an electrician's assessment of whether your consumer unit can carry it. Nothing else about the purchase is decidable until this is answered, and the answer sometimes ends the discussion.
Where it will stand
Non-combustible floor, able to take the weight, clearance around the machine, ventilation, not a bedroom, and reachable through the doors and steps between the front of the building and that spot. The last one catches people out with top loaders and narrow stairs.
How big your work is
Take your largest realistic piece, add the shelf and the props under it, and compare against internal dimensions rather than volume. Then ask honestly how often you will fill the kiln, because a half-empty firing costs the same as a full one and a kiln too large for your output is an expensive way to heat a garage.
What temperature you fire to
Earthenware around 1150, stoneware around 1250, with a margin so the kiln is not working at its limit every firing. A kiln rated well above your range costs a little more and lasts longer, because element life falls sharply at the top of the range.
Questions people ask about buy a kiln
What should I decide before buying a kiln?
The electrical supply available, where it will stand, the size of your largest work and the temperature you fire to. Everything else follows.
What costs are not in the price?
Delivery and positioning, electrical installation if needed, and kiln furniture, which is a significant separate purchase.
Is a bigger kiln better?
Only if you can fill it. A half-empty firing costs the same as a full one, so an oversized kiln is expensive to run.