I've noticed that if I've modified one of my (non-premium) vehicles then the price at which I can sell it for goes up. For example, I have an Ocelot F620 which has a normal sale price of $8000. I have since added a few mods to it (improved engine tuning, etc.) and now if I try to sell it the price offered is around $13000. (I can't remember exactly how much I've spend on the mods -- it was over a period of several weeks.)
So I was just wondering if anyone has ever bothered to work this out? If for example I spend $1000 on mods, how much does the price increase by? (it it that simple?) Are there any mods that don't increase the price? (like respraying?) Also, if I buy two mods in the same category (for example 'Engine Tuning 1' and 'Engine Tuning 2') does it just increase the price due to the more expensive of the two, or does it increase by some combination of the two?
I've tried briefly to figure this out myself, but the sale price of the car seems to behave in a strange way. I can drive my car into Los Santos Customs and check the sale price (by selecting 'sell', but not actually proceeding with the sale). If I then modify the car in some way, then check the sale price again, the sale price is unchanged! However, if I check the sale price of the car a day or so later (real-world time) the sale price has gone up to reflect the new modification. So I guess that leads on to another question: How long do you have to wait before car mods have an influence on the sale price?