He seems to be presenting it very honestly. Thats not an original TR3 color as far as I know. but the seller correctly states he thinks it was white with a red interior Also the engine has been painted blue at some point (it should be black) so that probably means a rebuild at some point, but that's not necessarily bad.
All in all it looks to be very solid and fairly rust free. deserving of a proper resto, but drivable now.
I would budget for rebuilding the hydraulics (brakes and clutch) He mentions a heavy pedal, and sitting dosen't do any good on rubber brake seals.
andyou should also be ready to sort out minor drivability problems and electrical glitches.
worst case maybe a carb rebuild, front suspension rebuild.
And even though he says the tires are rot free I would get a fresh set. It's not worth the risk.
This is all the commmon stuff that goes bad when someone only "lightly uses" a car. All the rubber parts start to crumble when they are put back into use.
if it's in drivable condition I would guess 10k would be a decent price 15k is pushing it a lot anything higher and you should wait for a better deal (but this depends on how bad you want a TR3)
Happy bidding.