At present, there are only the most cars in the used car market in Tianjin. But I suggest you go early. There are often intermittent attacks. I don't know when to check again. Located on the north side of Bei 'an Bridge, the exact location is not necessarily because it is mobile. Sometimes near the palace, sometimes in the square. (It seems to be in the square recently) Look for it yourself and see which one is crowded. As far as time is concerned, I suggest you make it 6 a.m.
Under Balitai Bridge, there are many bicycle sellers in the afternoon.
I don't recommend buying used cars because most of them are from unknown sources (that is, stolen). If you buy these cars, the problem of losing them may be more serious. Besides, cars are not cheap now. People who buy cars speculate on the price of cars.