It must be different where I live.
In my experience, there are three kinds of “thrift store”:
The first is run by a strictly local charity, with volunteers and gets donations that they re-sell in a church or inexpensive storefront. All proceeds to to the good works that they support. They sell to whoever wants to come in and pay the prices that they have set.
The second is a charity that collects needed things that low income families need. They want mainly things like furniture, clothing, especially for children, and things that a single mother might need, or a woman leaving a violent relationship. Things for people on the street are often needed too. Note that the first example above may ALSO run this type of charity - but they collect needed things for low income people, and don’t run their stores for them alone.
The third is larger “charities” that collect free stuff and resell it, with a portion of the proceeds to charity, and a large chunk to the board members and CEO’s who run the place. They also don’t care who buys their stuff, but they are much more careful to sift the good stuff out and get the most profit for it.
Bottom line - thrift stores in my area are most decidedly NOT like stores for low income people to go to for good deals.