Q: Can I give a fresh paint job to an old car to give the impression of a relatively new one? What about polishing or waxing a new item?

A: "One may not paint … old objects so that they should look new … nor may one soak meat in water to make it look white and robust." (Shulchan Aruch, Choshen Mishpat 228:9)

Thus, one may not try to mislead his potential customers by making a car look newer than it actually is. However, the SM"A (#15) explains that this refers to a case where the owner overcharges for an old item while the buyer is under the false impression that it is relatively new. However, if he charges a price which is fair for the old item and paints it just to make it more visually appealing, it is allowed.

Similarly, one may shine a new item to draw the customer's attention and make the item more attractive. Furthermore, if the new paint job actually adds value to the car, the seller can paint it and charge accordingly.