I am pretty sure that it goes without saying a crane with 5 inch knobby balls is a must in all fun centers (having your logo/mascot printed on them is awesome). They have been a staple for us for years. I have found that mixing one out of twenty with regional sports team balls is very popular. Put in a small smattering of balls with a ticket value and you have a grand slam!
I vend them for $1.00 play until you win and people will buy dozens to get a sports team ball or ticket value one. What a huge upsell that is!
The only place I have found these at is AA Global. I am pretty frugal and do a lot of shopping around but I have yet to find anyone that can beat them on any knobby balls.
Now if we could get hockey teams it would be a trifecta!