Re:
Jim, you're right that selling on more than one platform can end up putting a seller in a tricky position if there are offers made via both at more or less the same time. However, the correct thing to do is completely obvious - once you agree a sale in one place, it's no longer for sale anywhere else, even if you get a better offer.
The same dilemma can happen if an item is for sale only on RB - a sale is agreed on pm, then a higher offer comes in and it's exactly the same situation. Private selling is all done on trust isn't it?
When there's no track record of being unprincipled, it's unfair to suggest a seller won't be doing the right thing, so people should stop making groundless insinuations.
The OP has also not broken any rules, so just let him see if his price is too high, and revise it if he needs.