A chauffeur who works for a black car service says tips are essential to his earnings. Bernd von Jutrczenka/picture alliance via Getty Images Gig workers, from Uber drivers to delivery workers, say that tips are a big part of their earnings. One chauffeur in Florida said it's also true for his side hustle at a black car service. The job involves driving executives and pilots to and from airports, the driver said. This as-told-to essay is based on a conversation with Marcus Thompson, a…