I have knitted sweaters for our Yorkie and one for our Chihuahua. I knitted a camo hat & scarf for my hubby last year, so Dudley just *HAD* to have a sweater to match.
Angel (our Chihuahua) hates wearing any sweater. Dudley, on the other hand, loves his.
I have never thought about making them to sell. I do have the patterns around here somewhere. I will have to look around & see where I put my knitting & crochet stuff over the summer.