A $4k 4x4 will have a lot of years and miles on it. That has two implications for you as the next owner.
The first is that you are buying the previous owner's (or owners') maintenance habits at least as much as the vehicle, itself. If he neglected routine maintenance and bandaided what broke instead of fixing it properly, even a fundamentally sound design will have deteriorated into a POS.
The second is that, even if the previous owner was conscientious about maintenance and properly repaired everything that has failed so far, there are still many items that are approaching the end of their service lives. When, not if, they finally wear out, you will be the one facing a repair bill.
Unless you are a good mechanic yourself, your best defense against buying a POS is a thorough inspection by an honest, competent mechanic. If the seller won't agree to an inspection, no deal regardless how good the vehicle appears to be superficially. I wish I could recommend a mechanic for an inspection but the only place I know well enough to trust is in Papillion and only works on foreign vehicles.