How to find a safe crock

I know you advise to use glass jars and that is what I have done in the past, but if I am at a garage sale or even hardware store and see a crock, how do I know if it might be glazed (as in not lead glaze) safely. Also, do they absorb bad stuff, like if someone stored motor oil in it before they put it in their garage sale?

Don't buy anything from China!!! Just sayin.'

A friend in Vancouver has an electronics company. He sent a device (prototype) to be made in China. They sent it back to N.America three times saying that they had made changes to it. They hadn't done anything in actuality.
Chinese business and certification is worthless.

Your local potters will know better.