What to look out for when buying a used handheld?

Thinking of buying a used Vita from Kijiji because Canadian taxes and prices are outrageous where I live in Canada. I will obviously test it before buying it, but is there anything specific I should look out for that may not be immediately noticeable?

Obviously check the screen for scratches, but also to make sure the colour isn't faded. Make sure it can connect online. Check the gyroscope I guess. Welcome Park will be a pretty good test of all the different functions like the cameras, gyro and touch panels. Make sure it can read the memory card slot and also the Vita cartridge slot. Check the feel of the buttons to make sure they aren't loose or sticking.

Check the L/R buttons to see if they are responsive and work consistently when held down. Also, if it's a 1000 (non-slim) model, check if the L/R button creaks. I hear this is a common issue on the OLED models, including my own, although I took steps to try and fix it.