I have never done them on Ebay. No way to know if they are a legit break or not. I was first introduced to box breaks via card collecting forums I have participated in countless breaks on those all of the major 4 USA sports (baseball, football, hockey, basketball). I have even done some on blogs I have followed, and for my blog hosted a baseball break and a basketball break.
Stick with breaks from forums or blogs. With breaks on Ebay and such it is more expensive usually both in the cost per slot and the fact that you only get cards from that one slot. Even if there are some unclaimed spots. Breaks on card forums you usually get a bonus slot as they usually only have 10-15 people in the break with each person getting their purchased team and then getting either a totally random second team or getting the second team by a draft. Bloggers sometimes give you a second slot, depends on the blogger and the break.
It is best to only do breaks where you are familiar with the person breaking. On the other hand if you haven't done any breaks before, checkout the break hosting history of the host. Many break hosts on the card forums.
Some break hosts on the forums try to be super fair and if you go "hitless" they will send you some bonus "hits" from their own PC or from some previous break, so you might get a card from a different product than what was in the break and from a team you didn't have in the break. Sometimes even other people in the break will donate one of their hits to someone who went hitless.
Oh and usually forum break hosts are only in it for the fun of it, not the money so the prices per slot will be cheaper usually just enough to cover the price of the product being busted. Same with blog breaks. Breaks on Ebay and such (like many of the super breakers on youtube and other streaming video websites) you know they are just in it for the money. The cost for Ebay breaks will be higher and you could potentially get NOTHING out of it, not even some "lousy" base cards. I happen to like base cards and feel good about a break if I at least get a couple of cards.
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