But he's Chinese, so we shouldn't ban him, just to avoid conflict.

You're judging from your perspective, not from the perspective of the Chinese.

In the Russian mentality, the cult of the warrior occupies a prominent place, with all the concepts that follow from it. And in the Chinese mentality, the cult of the merchant occupies that place. Therefore, they interpret concessions as weakness, a reason to try to bargain for something else.

If we don't ban Tinker now, it will be a signal to him and other Chinese players that there are gullible fools here who can be led by the nose. I suspect they already think that way, so I recommend studying the games of other Chinese players; the situation is likely to be similar.

So, don't worry too much about "avoiding conflict"; merchants perceive the use of force as setting the rules of the game, establishing the boundaries of what is permissible, etc.

And even if we do end up arguing, it's not a big deal; it's much better than allowing a cheater to win the tournament.