Been there, done that. Used carbs are not often what is seen in the description. I've had several different types, most needed some work or parts replacement. The worst ones showed wear in areas that require major components, making repairs exceed the value.
The biggest headache is the price of genuine brand name parts. I'm old school and almost always use original equipment parts, except in places where it's not critical and easy to replace. Some of the stuff is just plain cost prohibitive on our older models.
I've been fortunate to find good replacements when needed, by being diligent in my search methods. It's not always fun, often very time consuming but is usually the best option.