How does one ask for a raise without sounding desperate or an asshole?

When talking to your client directly : yeah that tweaking will be done, but can u talk my boss into promoting me , I will give u additional services for the next 1 month and won't charge it"

Find a better paying job.

I'll be interested to see what others answer as well. I tend to come off rather pushy & bring up wanting more money every chance I get. I'm not sure it's a very effective strategy overall.

Has anyone taken any of the formal classes or workshops about techniques for asking for a raise or finding a better-paying job? I've often wondered if they are worth the money (most are rather pricey) or are just a hand-wavy, double-talking waste of time.