most of them are thrashed whether they have mods or not.
i got my car with heaps of mods and saved a stack. i've seen ppl buy stock cars for the same price that i got mine and they are even older cars in some instances.
put it this way, after buying my car i wouldn't have $15k to spend on mods so i'm gratefull the previous owner spent that amount. who cares if they are slightly used, you save more than enough to pay for your insurance for a few years.