Qitzur Shulchan Arukh 62:4
One who has some item to sell, is forbidden for him to beautify it in order to thereby fool [prospective buyers]. For example, [it is forbidden] to feed an animal bran-water to make it swell, or straighten its hair so that it looks fat, or to paint an old pot so that it looks new, or anything else that derives from this [principle].
A straightforward truth in advertising law – you can’t misrepresent the product. What I personally found this interesting is that in 62:1 we ruled out selling the item overpriced. So this appears to be saying that even if one of these subterfuges is done in order to make the item easier to sell for what it’s really worth.