To use figures already mentioned for the tip scale it seems to range anywhere from 15% to 35%
Get a cheap meal and spend $50, get excellent service and tip 35%. Tip = $17.50
Get an expensive meal and spend $150, get crappy service and tip 15%. Tip = $22.50
So you decide to eat an expensive meal and received crappy service you still ended up tipping more for the crappy service than you did for the cheap meal with excellent service. This is one reason why I dont think tips should necessarily be based on a percentage scale.
Get a cheap meal and spend $50, get excellent service and tip 35%. Tip = $17.50
Get an expensive meal and spend $150, get crappy service and tip 15%. Tip = $22.50
So you decide to eat an expensive meal and received crappy service you still ended up tipping more for the crappy service than you did for the cheap meal with excellent service. This is one reason why I dont think tips should necessarily be based on a percentage scale.