I would say also check whatever website for the country you are looking in for something like the Better Business Bureau (u.s.) If there are a lot of complaints.... well, speaks for itself. Your idea seems sound, 10+ years and positive feedback is a good start. I prefer regulated myself, but it isn't mandatory imho. If you begin to narrow it down, to say 4 or 5, then search those particular firms with your google-fu, such as (Samplebroker problems; sampnlebroker scam; samplebroker success) etc. It could give you a better opinion. I would also not ivest too much money with them at first until you are certain of them.
Just my 2 cents :)