Here in Australia we have the "Salvos" and "Vinnies" and many other "op shops" that sell old stuff people donated, and we have "Cash Converters" who buys your stuff when you need cash fast and resell it to the public.
In Japan there is a huge chain called "Hard Off" and several other variants plus competitors mainly known as "recycle shops" (リサイクル) these days.
In much of Europe there are flea markets, which might only run on weekends.
But even though I've spent six months travelling around Taiwan over two trips I don't recall ever seeing anything similar, except perhaps selling only used furniture or appliances/whitegoods.
I suppose they exist and I just don't know what they're called and how to find them. They're probably in low-rent areas of city outskirts?
Does anybody know what such places are called in Chinese in Taiwan, whether there are any big chains, whether there are brick-and-mortar stores, or more like Sunday markets / car boot sales on weekends?
(I'd mainly be looking for early '80s clone computers. Oh and I do know two ways to say "used" or "secondhand" in Chinese are 中古 zhōnggǔ and 二手 èrshǒu, but I knew that last time I was in Taiwan and didn't find any thrift stores.)