I've read occasional mentions of black markets that existed in Communist nations - for example, of collectivized farms that kept one set of books for the authorities and another that reflected illegal exchange with trusted community members.

What are some good written or verbal accounts of such private trade that went on in defiance of collectivization? I am guessing there was little documentation kept at the time, due to the underground and highly illegal nature of trade. But, maybe something exists in the form of memoirs or interviews?