Most decent locksmiths keep a stock of locks in their possession - after all, they are called out for emergency work and have to have a stock of necessary parts. I think he might be pulling a fast one and he has given an incorrect diagnosis of the problem. If I was your neighbour, I would tell him that the problem has been identified as a slipping plate and new locks are not required. If she feels daunted at the prospect of telling him, she might want to get her friend`s son or someone else to do that.