I only noticed the problem now (stopped playing for a couple of months) and am totally despaired, my favorite household actually relies on these yard sales to make money (it's a challenge house, so very few options are allowed), they do have a bit of money to last but they better patch this bug soon!
It's as the others described, everything is normal, except that customers never buy. My sim tends the table normally ('you shuda! you shuda!'), customers come, check the wares, chat a bit then leave. I tried at different time of day, tried different things for sell, nothing works. Okay my sim is hot headed and often autonomously fight with one of the customers and beat the * out of them, but still!! Before they broke the table, all the customers always bought something before leaving and be replaced by another spawn.
Please EA, think of the poor families - they'll only last 3 bills if I counted correctly.. Repair that table! ☹️(