When I am truck shopping, any modifications or evidence of a tuner and I walk away.
Suspension lifts always put additional stress on components. Plus, if they are done incorrectly, they can put a lot of additional stress. Tuners, etc. do the same thing to engines.
Sure, there are 'some' who did it right, used top end parts, etc. But I don't want to spend the time to figure it out. Buying a used vehicle is a******shoot already - I don't want to add additional points of possible failure!
Plus, I don't want a lifted truck. Usually people are trying to sell their modifications as added value, and thus asking for a higher price, and to me, it is actually a negative because I don't want it on there. So, it is usually worthless to even try to negotiate.
