1. Check the maintenance records by taking it to a Toyota dealer to see when the last scheduled maintenance was performed. If the owner did not take it to a dealer for service, ask him for the oil change and related service receipts.
2. Have the car examined by a mechanic that you trust.
Toyotas have perhaps the most solid and consistent reliability and dependability track record of any make available in the United States, but you should verify how its owner has treated it over that 100K miles, which is extraordinarily high for a 4-year old auto (an average of 25K annually compared to a 'normal' average of 15K).
If it is a rental car (ie you are buying it from Hertz or some such) then I would stay away.
And welcome to A2K.