Buying a used prop
Buying a used propeller is a challenging task because if you take a look at the websites which sell used props or go to a shop for this purpose, you will be simply overwhelmed with the choice available to you in terms of their makes, shapes, materials, size etc.
Since there is a high probability that you might end up buying a wrong prop at the first instance, the very first thing you should ask the seller is whether they offer a replacement assurance in case the prop doesn’t work with your engine.
When I say working with your engine, I do not only mean physical fitting. Any propeller with the right diameter compared to the shaft of the engine would fit in it, but that does not mean that it will perform its function in a proper manner.
Many props are made specifically for some specific boats and they only fit and perform in those vehicles. You might find a lot of useful information regarding what sorts of propellers might fit into your boat, otherwise you might want to experiment a bit by trying couple of changes.
The material of the prop is also important in deciding which one would be the best fit for your boat. Commonly used materials include aluminium, composite materials etc. another possibility is to use a prop which can blades that can be replaced individually instead of replacing the whole propeller, though you must realize that in such a case you would need exactly the same blade as the other ones, hence it might not be worth buying except when you have no other option.