A family claim they have been “tricked” after finding out a dog they bought on Gumtree needs surgery costing £14,000.
Black labrador Maya was purchased for £500 in June by Sophie and Paul McDonnel.
The couple, from Walney Island, Cumbria, said they quickly realised the pup wasn't well after spotting she was underweight and riddled with worms.
The McDonnels then took Maya to the vets, where they were told she needed two full hip replacements at the cost of £14,000.
The couple, who have a young son, think the dog had hip problems when they bought her.
Sophie had thought she was getting a bargain when the seller told her she could have Maya for £500 after being advertised at £1,200.
The pup, their first, was handed to them at the gate without papers, food, bedding or toys, Sophie claims.
She also weighed only four kilos at nine weeks old – when she would be expected to come in at around nine kilos.
The dog, now nine months old, began limping and whining all the time in October and can now only manage a ten minute walk.
Sophie, 28, said: "When we were driving home we were so shocked by the experience. I feel really bad and also stupid like I’ve been tricked."
Maya currently can't climb the stairs or squat to go to the loo and takes six painkillers daily as she waits for the operation.
Sophie and her husband Paul, 38, are asking for donations as they can’t afford to pay the bill.
Their insurance policy has a £3,000 limit per year which is currently being used for x-rays and medicine.
Customer relations worker Sophie added: “It's heartbreaking. She's such a loving and fun dog. It's horrible to see her in so much pain.”
"She's on a massive dose of painkillers and she's so young. It's about her quality of life.
"Without the operations her hips could totally lock at any time and she won't be able to move.
"That leads to arthritis, and her quality of life could become so poor we'd have to have her put down.”
Vets diagnosed severe hip dysplasia in December and have told the family Maya's surgery needs to be done by March.
The condition – more common in larger dogs – is considered to be one of the most serious problems in dog breeding, studies say.
It is hereditary but can be eradicated by selective breeding tactics such as screening of the parents.
Sophie says she has reported the seller to the RSPCA.