Another take is that if workers are able to say no to a shit job, then the burden is placed on the employer to either eliminate the job or make it less shit.
In the Nordics, there are no manual car washes, yet life goes on. Economically it doesn't make sense because of the high labor costs, and realistically it is a menial job that can be for the most part automated.
If you want to live in a world where you can have a cheap hand wash in your back yard, then you have to also admit to wanting structural inequalities to keep people trapped in those carwash jobs. It's delusional to believe that the people washing your car have a path out through hard work alone; my observation is that they already work pretty hard.
UBI is much more about giving workers power than giving them free money. And yes, there will be dole bludgers. Unfortunately any system is going to have inefficiencies, you just have to pick which ones and live with it. Alternatively, you can get tough on crime and house a prison population.