That generation of the Avalon (model years 2000-2004) only came with the 3.0L V6 (1MZ-FE) and was susceptible to oil sludge and oil burning.  There was even a class action lawsuit against Toyota for that issue.  One way to mitigate that issue was religiously changing the engine oil on time every 3,000-5,000 miles (and using only the proper oil meeting Toyota’s specs).  At 200,311 miles I would want evidence the previous owner or owners were on top of the engine oil changes (it gets harder to track when a vehicle has multiple owners).  Otherwise, I would walk away as you don’t want to inherit an engine with sludge and oil burning.  Also, that engine had a timing belt and recommended interval to change was 90,000 miles, so if it didn’t have that done you are looking at additional $$ to get it replaced (budget for that).   Also, make sure the transmission fluids were changed on time.  See below for other issues but that’s the big one, and at that mileage it can become a money pit if it was not well taken care of.  Additionally, not sure how many years and miles you need the vehicle to last you but you could be dumping more money into the vehicle at that age (nearly 20 years) and mileage than the vehicle is worth.

http://www.toyotaproblems.com/oil-sludge/

https://repairpal.com/2002-toyota-avalon/problems

They are very reliable cars. I'd compare the Avalon to Lexus sedans. But the high mileague is a concern. Not that high mileague is bad, but you don't know the history of the car under previous owner(s). Of course, they will tell you they have taken good care of it.