Can I sue for Harment and Extortion?

Can I sue someone for repeated harment and blatant extortion? The situation is as follows: A man asked me for help with his website. The request was for setting up a shopping cart that he could take orders with via the web. He repeatedly emphasized that "the best deals are made on a handshake" and thus we have no contract but had a verbal agreement that I would be paid 10% of gross sales that the site produced. The shopping cart software that I had him purchase was unfortunately too advanced for his current web hosting service and I politely offered to host it on my personal web host for him until he got a new server provider. Ideally I just wanted to be paid for doing some coding and installing the shopping cart. The man stated that if I didn't want a percentage of sales, he would pay me $500 for the work I had done and we would part ways. After a few weeks of getting to know this guy, things seemed more and more shady.