I would say avoid things on major sites like Ebay (which at one time the breaks were against ebay rules on gambling), craigslist or even on Facebook (for me facebook is only social media not business stuff, trading cards is a hobby that is also part business when it comes to group breaks).
I have only joined group breaks that were on trading card forums and I tend to stick with ones from members of the community that I have known about or have observed how they run their breaks. Some break hosts will be as fair as possible and sometimes will send bonus cards for people whose teams didn't provide hits in the break.
Stay away from hosts who seem to be only in the business of group breaks, or have a ton of breaks going on at the same time. Some of them might be legit but many of them are soo caught up in the business end they don't care about anybody in the break. Also if they are doing multiple breaks every day how do you know the cards you receive will be from the specific break you signed up for?
Also watch how the breaker films their breaks if you only see the guys face and rarely any cards, they might be trying pull something or hide some of the big hits and try to keep them for themselves to sell elsewhere.
I collect: Baseball, Football, Hockey, Mostly Vintage pre1980, My Homie teams - Washington/Baltimore Teams Senators (Twins, Rangers), Expos/Nationals, Redskins, Capitals, Bullets/Wizards - HOFers - Non-sport (mostly TV shows and movies).
My Trade List is very much a work in progress
CaptKirk42s Trading Card Blog Curly W Cards Strive For '65 YouTube klandersen42