How to block [?] from accepting game request?

It might be better to use a synonym to block, in this case restrict. Thanks for pointing this out. Thanks also for reiterating these precautions, though they were already in place.

The rank of a [?] becomes within the range of being even strength to a sdk by a single win, be that with a win over another [?] or a sdk. This makes the [?] player in question a possible actual strength of 25k-9d. There is no way to tell this from a single win from their part. If it were the first time a [?] accepted the game request it would not have been asked.

As has been answered before, it is not possible to block [?], which was all information needed.

In retrospect it would have been better not to ask, having been called nasty words for even suggesting not playing [?] player. One can only assume they are active players who speak from a place of experience on the matter of playing even opponents regularly and often, and judging playing [?] opponents as a public service all should partake in.

Thanks to all for input and advice, most of all thanks for short and concise answers.