Welcome to FRF, Rivermom!
Which model are you looking at? Shamrock had a bunch of models from back then ranging from 17'-26' long and with different floorplans. Here is the NADA page that may help you 2002 Flagstaff Price, 2002 Flagstaff Values & 2002 Flagstaff Specs | NADAguides
Depending on your locale, the trailer model and its "true" condition, the price they are asking is probably fine. Here is a site you can use to search out actual sales - RV Trader
As for the water damage - I would personally walk away from anything
with water damage. I know its tempting to think they completely fixed the damage and fixed the source that caused the damage, but I don't like the odds. And, I'm too busy to buy a "fixer-upper". YMMV and you have to decide how handy you are and how much time and effort you are willing to put into this thing if it turns out you are buying someone else's problem.
Glad you asked and I'm sure others here will have thoughts to share, as well.