What is the law on abandonment of an item?

I sold a tanning bed approximately 2 years ago for cash money of $700.00. They were to return in a couple of days to pick the bed up but never came nor called to reschedule. They finally called back about a year later and I explained I still had the bed, did not know what had happened to them, did not know how to get in touch with them, but they needed to pick the bed up. I also gave them my father and my brother's name and phone # in the event they could not come on the set date since I work and go to college. Again, they did not come nor call for another year. I had sold the bed about 2 months before they called the 2nd time, which had been 2 years from the purchase date. The man became irate, demanded his money that day, demanded to know how much I resold the bed for. I told him I was on my way to college and besides he had abandoned the bed for 2 years. Since then he or his wife has called daily, left rude messages on my answering machine, and demanding their money back immediately. They certainly did not show this much concern nor energy while I held the bed for 2years and it took up needed space for 2 years. Do I legally have to give them their money back or did they abandon the item?