We have seen quite a few fake high-end watches in the thrift stores. We stay away from those. However, there are a lot of watches that the thrift stores do not recognize as high-end and are good to look for. Some clues are stainless steel or non-reflective black steel watch, additional dials such as chronograph or day/date. The thrift stores often mark watches up, regardless of actual retail or resale value. And they often do not differentiate between the higher-priced versus lower-priced styles. There are many Seiko watches worth buying. They are marked with a model number on the back, and the value varies greatly depending on the particular model.
Seiko 7T62-OAMO Chronograph watch 100m stainless steel
Tissot Seastar men's bracelet watch