One other reason to be concerned about an altered vehicle, is future maintenance can be made beyond beyond frustrating without knowing precisely what was done. Emissions and engine control systems are often modified along with the bolt-on parts. While the average inspection will find bolt-on alterations, programming changes will remain hidden; and can ruin an engine faster than any bolt-on.
Also, what is "an upgrade" is in the eye of the beholder. I bought an all aluminum radiator thinking it was "an upgrade", except that "upgrade" didn't even last 5% of the time that the OEM part was in the vehicle.
My prior vehicle had an aftermarket radio installed. When it died, I found that a prior owner cutout the vehicle's wire harness. Instead of adapting the radio to the vehicle, he adapted the vehicle to the radio.
That meant I had to obtain a wiring harness, wiring diagram, map out the conversion, confirm the function of each wire with a multi-function volt meter and D-Cell battery (for the speakers), then finally solder over a dozen wires. When that radio was stolen, I had to stick with the same manufacturer to avoid a repeat experience.
Bottom line, if you enjoy
driving a vehicle, don't by altered. If you enjoy
looking at your vehicle... on jack stands potentially.... buy altered.