Bingo ROI?

36%

Online bingo can be a very expensive game.  Cheap to play but very high variance.  You could easily go say £1000 before seeing anything from £100 to the biggest prizes back.  Club bingo like Mecca/Gala smaller prizes but you won't lose as much if you play weekly for a year.

I would guess around minus 20% ?

you just need to ask the operator what the house take / rake is... this will be the same as ROI (assuming everyone who plays can actually play properly, so add a little bit back to make up for this depending on how many idiots you think play bingo).