​Client wants a refund

A client came to see me after getting ‘rooked’ by an undisclosed company about a car stereo. He didn’t like the OEM radio so he found one on ebay and had them install it. Then he didn’t like that one either so he had them uninstall it. Ff a month and we pick out a $450 stereo and he asks to take out the OEM radio and install a new one for $50 labor. A few days later, he calls 4 times on a Saturday when the shop is closed and says he doesn’t like it, it doesn’t work, his GPS is sending him down wrong ways, the screen isn’t bright enough and he wants a refund. I am so tired of dealing with this guy’s half witted humor and side stories that I want to give him a refund and he can keep the radio. Is this acceptable? Do I need to re-install the OEM? He has it. I don’t want to touch his car again as he told me he was going to call his lawyer and if I didn’t give him the $500, there were “other ways to get it”.