It isn't just a matter of the wood catching fire. It depends on what the wood is, I have seen oak charred, yew seriously burnt and pine with a good few mill. deep charring. Add to that the fact that there is a good chance that the wood will have been oiled or polished, possibly varnished or lacquered and you have a potentially highly inflammable substance in contact with a hot metal. Not exactly a good or safe combination. It may well be fine some of the time but it only takes one incident to ruin someones life. Not an acceptable risk. Also, if you are selling your work you are morally, if not legally obliged to make sure that any and all risks are eradicated as far as is possible. I am afraid that I see food utensils made from laburnum and yew (but the poison is not usually in the wood!) Goblets finished with all sorts of oil, candles and t light holders with no inserts all for sale at craft fairs and I am sorry but to me that is just as bad as the foreign imports that we all decry. No brainer. If you are selling do it responsibly.
Pete