You can prepay your tips on Disney. I budgeted the recommended cost into my budget, and it was the same as what Princess had recommended (per day) on our cruise there last year. We prepaid for both. On the Princess cruise, we had an exceptional room steward, and gave him additional in cash. On
DCL, we found our serving team to be exceptional, and tipped them additional in cash. I don't mind tipping, it's part of the expense of cruising. Just like tipping in a sit down restaurant. You can choose quick service restaurants or sit down, but everyone knows the expense involved.
Frankly, for the cost of the meals each day, I would have paid more in tax and tips eating that way at WDW! For example:
Our lunch at Coral Reef for 4 (DD11 counts as an adult, DS8 ate from the kids' menu) was $120, before tax and tip. The 20% tip is $24. That's $6 apiece right there, and I would wager my dinners on DCL far exceeded the cost and quality of that meal. My character buffet breakfast at AK was $85 for the 4 of us. Even giving that server just 10% (I didn't, I gave 15%), that's $8.50. Again, another $2+ apiece. Not including tax. Now, with just 2 comparable meals I'm already up to over $8 pp/day, and that's before the stateroom host, (who did far more in terms of cleaning, tidying up, turn down, etc than mousekeeping did at WDW) gets a tip as well! So I think it is exactly the right amount.
If I encountered poor service, I'd take it up with a supervisor right away, and give them an opportunity to make the situation right. The cruiseline wants their employees to genuinely give good service. That's what keeps customers returning, and that's the bread and butter of their business.