Do I have to accept every job I am offered?

Not usually. The freedom to turn work down is one of the things that makes an arrangement genuinely self-employed rather than employment, and platforms lean on it heavily when describing your status.

That said, several of them track acceptance and completion rates, and a low rate can affect what you get offered or, in some cases, your standing on the platform. The freedom is real; it is not free of consequence.

Cancelling a job you have already accepted is treated very differently from declining one. Declining costs you nothing on most platforms. Cancelling repeatedly does.

From a purely commercial angle, learning which jobs to decline is most of the difference between a good hourly rate and a poor one. A long-distance drop for a flat fee is the classic example.