when you go to a sealed booster tourneys, do you usually get to pick youre own boosters or does the store owner pick them for you?

It depends upon the venue. My particular venue will bust open a case for a large tournament (say, a Marquee), and will let you pick your boosters. On smaller tournaments, they will pick the boosters for us since they normally keep the HC boosters behind the counter. The owner will just grab some and give them to you. But that is my venue... I'm sure you would be allowed to pick your own boosters.

Where I play, you get to pick your own boosters. They are kept behind the counter, but the guy working there asks which ones you want.

the only reason I asked is because I played in a Marquee the other day, and the store owner just reached into the box and pulled out 3 boosters for me... and personally it felt like a huge part of the tourney was ruined, because I wasn't given the chance to use my own luck.

It usually simply depends upon weather or not the store keeps the boosters behind the counter. At one store I go to, they are kept on the shelf, and we pick for ourselves. At a couple of others, they are kept behind the sales counter, and are chosen by the staff. In my experience, the odds have usually worked out better if I DON'T pick them myself.