I used BTCRobot and I am an affiliate of theirs. I'm not a customer anymore as I've found that its more profitable for me to leverage trade on BitFinex.com than to make use of the platinum license.
Its not a scam and I can vouch for it (on that aspect) from my experiences. For accepting payments, they use the services of Clickbetter, a Clickbank clone so you're assured of your money back if you make a refund request.
In essence, as I could tell it uses the price difference between the exchanges to decide if it should buy or sell and makes a few small trade when it claims to find opportunities. I bought in a time when the market was a bit flat, not much volatility and hence not much trading activity from the bot.
When it did trade, it was counter-intuitive. Selling when the price dropped and buying when it went high again.
All the while though this, they kept in touch with us customers assuring us that this bot is a long term thing and in the long run it would turn out well but it simply wasn't working the way I wanted an automated trading bot to do so.
As others have mentioned on this thread, there are some open source bots and I'm going to start there, do some research and find a system to trade that we can discuss and collaborate on, make available to the community freely and sponsor upgrades through donations, because it works to grow your BTC (XBT?) wallet

Anyone interested please PM me!