Some clients tip and some don't.
Yes you should pay more to host because it takes time for the escort to get to you, that's why outcalls are more expensive than incalls.
That's a good reason to tip, someone gives a better than expected service.
Superior client? This ain't frequent flyer, you don't get Subway tokens for a discount later, unless you hire him a few times a month and the 2 of you agree something like this.
Have you underpay/stiffed any escorts? Sounds like you're suggesting that.
I never heard of someone asking for a tip in advance. They just want to get paid X for their service.
Amateur: some would call them fresh, not jaded. Btw I only hire professionals but I'm sure all of them at one point in their lives were amateur. We all had a day 1 in many jobs.
I don't know about escaping... but unless is late at night and the client looks wasted there's no excuse to ask for upfront payment.