Start with the exact model
A familiar camera name can hide several versions. Check the model number, mount, and serial markings before assuming a lens, finder, screen, or flash accessory will fit. If the listing includes a box, compare its label with the item inside.
Separate cosmetics from function
Paint loss and scuffs may have little effect on use. Haze, fungus, oil on aperture blades, sluggish shutters, corrosion, and damaged contacts deserve more attention. Ask for clear photos in ordinary light and a plain description of what was actually tested.
Count the small pieces
Caps, cases, screws, adapters, and original packaging can be surprisingly hard to replace. Check whether each photographed accessory is included, then compare the total cost with a complete example. A good listing should make missing parts easy to spot.
Buy for your purpose
A collector may value original packaging and matching finish. A photographer may care more about smooth operation and clean optics. A repairer may welcome a parts body. Decide which of those you are before paying a premium for the wrong thing.