It really depends on your comfort level and the price and obviously the actual damage. Our motor home was a shallow fresh water flood (the person who had the accident said it reached the bottom of the entry door in the front and the rear wasn't in the water (the motor home was sold at auction by the insurance company, I just manage to track down the previous owner to ask him some questions. There was no incentive for him to hide anything)).
There are some minor issues although none of it seems to be from the water itself (it was also crashed through a guardrail before it got to the water and that caused some damage) but for me, the price was worth it (I paid about 1/4 of low retail but it does have a salvage title). There is some rust on the frame but it really isn't nearly as bad as our previous mh that wasn't a flood. I don't actually see any issues on ours that are actually from the flooding.