Well more of the pros come from the US. Usually american footy and bball. They don't just bet sides, they bet totals, quarters halves, props etc. These US sports also have many more teams, allowing for more betting opportunities.

Alot of pro's don't watch games at all, they rely on stats, trends, line movement, shopping for lines etc.

Also depends what you want from your sportsbetting. Would you be doing it as a hobby or for profit, and if it's for profit, as your major source of income or just a supplement? What sport/s would you be betting?

"Would they rely on a few tipsters,"

Usually not. Most handicappers probally just play their own picks. Most 'tipsters' are frauds or just aren't profitable longterm so it's usually better to stay clear from them.

HOWEVER, if you find a source of picks that is profitable longterm, you'd be a fool not to bet them (it's free money). Course most people can't do that because finding a good source of picks takes time and effort.