I saw some on the contest can able to hit more than 500x free spins in small bets. I have never hit many free spins; my maximum is around 40x, and most slots games are restricted in my country, that's why I can not participate in any contests due to the limited slots games.
Yep, people even hit 900x, 1,000x or 2,000x but this certainly mostly happens with very high volatility games. Also, the more one spins the slots, the higher the chances of hitting a high multiplier at one point or one day.
This means you need to have some good balance in your account just in case you are to go for let's say 1,000 to 2,000 spins without any big multiplier win.