If you asked the average paid Americans if they would work 5 hours for $300, I'd guess the majority would say yes....
Except for AF member appraisers....
Your statement is too simplistic. First of all we don't make $300 for five hours of work; we have expenses. Let us say that is 20% for round numbers. So we are down to $240 for that five hours. Then we have to pay our own side of SS so subtract about another 7.5% and we are now down to ~$220. Most employers offer a 401k match, subtract another 4% so we are down to about $210 for that five hours of work which is $42/hour.
A plumber or electrician around here gets about $35/hour and of course anything over 40 is OT. In addition to that $35/hour they get benefits including retirement. I am told that is worth about $15/hour. The electrician/plumber make make less per year than I do but their total compensation is about $50/hour while you example leads to about $42/hour.
Additionally there is RISK. Every smart business owner takes into account risk and measures that against other opportunities like a regular job (opportunity cost). We have to take into account that we might lose a major client or maybe 2008 will happen again. People working for employers generally don't have the risk of the employer.
Then of course I have to maintain a professional license, take CE classes and maintain my business like trying to collect from deadbeats, paying quarterly taxes, doing some of my own accounting, marketing, etc. So, while that five hours grosses me $300 I have other hours in my business where I get no compensation.
I will compare that to my wife's profession, nurse practitioner. NPs make $40-$70/hour depending on experience and specialty; obviously some make a lot more. She has to take CE and has to maintain two licenses (state NP license and her DEA License to prescribe narcotics). The employer pays for all of that. Additionally they pay her her paycheck to take the CE classes (she gets a week of paid CE time), the transportation to CE and the hotel room and meals. How much is that worth?
She gets a 4% match on her retirement, has great benefits including health care. How much is health insurance worth that is mostly paid by the employer? How much is her four weeks of vacation time and one week of sick time worth? Is the appraiser making $42/hour or a lot less when we add in all the things we don't get that similarly paid professionals make?
$300 for five hours work is very misleading.