[Panda Bear]

I agree, except for obvious abuses, requests should be honored.

As base ump, regardless of position, part of my job is to be a resource for appeals for assistance, checked swings included. Depending on circumstances, sometimes I'll be a better resource than others. But, as with any request for assistance, only change the call when asked if you are sure.

There is no harm in asking, essentially, "Did you see something different?" If the answer is "yes", then you saw something different; rule accordingly. However, a "no" answer could be a)you saw it the same OR b)you didn't see it well enough to tell if there was something different or not. In case b, you stay with the original call.