These cars are often "reconstructed" vehicles, a Frankenstein'ish welded together combination of sections of multiple identical model cars, each of which were involved in serious collisions, and creating a whole car.
Despite what most people think, not all "salvage" cars are reconstructed. Some were stolen and recovered in good physical condition. Some experience other serious events that causes an insurance company to pay its owners the insurance valued amount at some point. However, the most treacherous "salvage" vehicle to avoid is the reconstructed one. It may become the love of a car buyer's life, and all may seem good and right to the buyer for days, weeks, months or years. But if and when the car is involved in a collision, the multiple welds means that the structure is not able to properly absorb the crash impact to protect the car's occupants. As a result, many reconstructed vehicles will buckle twist or even break apart in a crash, putting every occupant at serious risk of physical harm or death.
When everything seems a bit "too right", don't assume that everything is right or for that matter, wrong; There's always some lucky joker to beat the odds and win a big lotto pot; your luck may let you score an extraordinary deal on an underpriced car. Just don't rush or act impulsively, which are common causes of many car buying victims' woes. For me, someone whose negotiated more car deals in a week than most negotiate in a lifetime, my policy is that the next time I'll rush into a car deal is if when find an $80,000 Porsche cabrio offered for $500 by a spurned spouse trying to get her pound of flesh.
You have a nose to smell food before eating, a tongue to taste before swallowing, and a mind that should give you a funny feeling when something seems a little be better than you ever expected. Use those abilities to check out any deal carefullly whether or not there are asterisks in an advertisement. And if you want to buy a car, always put the car through a complete and thorough mechanical and structural inspection by a tech who knows what he/she is doing, that you had paid to tell you the truth.