Most of the companies frown on baiting for tips these days. When I flew there, (for 7 years), it was frowned upon asking for tips, so we just put $20 clipped onto the dash.
I kept taack of mine and averaged $70 per day, but you could easily go a month with nothing and then all of a sudden get $200 to $300 a day. Do not rely on them though---and ALWAYS tip out your ground crew, they can make your life difficult.