However, to accept and then cancel affects your CANCELLATION rate, which is a metric that Uber also keeps track of.
Both are looked down upon by Uber, but accepting and canceling is worse than simply not accepting. The acceptance threshold is 80%, whereas canceling more than 10% of accepted requests will warrant a threat from uber, which makes sense since it significantly impacts the rider’s experience (remember waiting for a taxicab that only never shows up to your home?).