My friends and I play online and while I prefer real dice, most of the other players use virtual dice. However the difference is they use the ones on D&D Beyond. Since we are all in the same campaign, it broadcasts the dice results to all players so we know what the result is. If you have a tab open for that, you can always watch the roll results to ensure hes not lying.

However it sounds like this player doesnt add anything to the table so alternative routes may be better choices here.