As said above, an A500 has the by far the best compatibility for floppy based games i.e. what you will be purchasing via eBay.
An A500+, A600, A1000, A1200, A3000, A4000 may
have issues due to the different Chipsets / Kickstart ROMS used in these models... The only way to virtually guarantee compatibility with these models (minus the A500+ / A600) is to use a HDD and WHDLoad