You need to see it in person. Check the inside ceiling and walls for any softness, mold, etc. Remember, that a leak in the roof could show up in a different spot inside depending on how the water flowed.
Signs of prior leakage aren't always a "run away" sign. Sometimes, a leak happens - to any rig. It's how quickly the leak was repaired that matters. It also depends on how much you love the rig.
There was sign of leakage at my A/C and ceiling vent in the clipper. I checked the areas, including nearby walls, for further signs of damage, and when I didn't find any, I decided to go for it. Before the first rains, I resealed the roof. The first rain, I stood inside the clipper and watched. No leaking. I would have lost out on a great RV if I had just run away.
And there's no reason why that RV with no signs of leaking ends up leaking after you bought it.