A.L.
If they haven't, they should get a few different quotes. That will give you a an idea of what a fair cost for the project is.
If they have gotten a number of quotes and they were all in the same ballpark (or they picked the one they liked best, even if it was more expensive) I'd say they've done their homework and there is nothing fishy.
My inlaws are in their mid-seventies, but let me tell you, my FIL who used to be a salesman is still excellent at negotiations like that.