That may be the dumbest thing you've said yet, and that's a level that's difficult for most to obtain.
You're the one trying to sell your truck. Obviously you want to get as much out of it as you can. If you think something on your truck is going to increase its value, you're probably going to list it. When you say something is custom (whether or not it actually is), you're stating to the buyer that it is something they cannot find elsewhere and therefore they should pay a premium for it.