some Petcos carry morphs you wouldn't expect to see the one 25 minutes away from me carries BELs and pieds from time to time, and once had a Visual clown available for $900.
I'm not sure about the lump but it resembles (from the side) the lump i saw on a breeders BEL hatchlings. He had three out of five eggs come out as BEL's and 2 of them had a lump on their ribs. He had taken them to the vet who said not to worry but they don't know what it is. He was selling them for $300 as pet only, no breeding just in case. Mind you, he didn't have any proof he took them to the vet, and the lumps were hard and immobile, and clearly visible no matter what position the snakes were in. They eat though and have shed, as when I looked at them, they were a month and a half old and it was on feeding day that i went so he gave them a mouse each and they took instantly. But their lumps were bigger and spanned their entire girth, whereas it looks like yours is just a point on the side.
Needless to say, I walked away from the sale. $300 was something i didn't want to spend at the time to just take it to the vet to get it for sure known by me checked out, yknow?