most providers say tips are not required but appreciated.  what % if any do you give.  I usually do 20% for normal service and  
30% if true GFE

This supposes that the service was very good or better

My attitude is that the ladies set their price and for me I consider the tip built in.  I often bring a bottle or two of wine or something else to drink.

I've tipped a $50 bill to a new provider that I probably will never see again and & a $80 bottle of single-malt Scotch to a regular, but I tend to think repeat business is the nicest tip. It just depends how my budget is that month.  

I don't tip, but I do take a gift, and no one has ever expressed disappointment over candles.  As others have said, the best tip seems to be a repeat visit.