It might take time for a sportsbook provider to realize that username "holy" on Rollbit is the same person as username "darkness" in, let's say, BetPanda, and UID 12345678 on BC. But eventually algorithm will caught them, and thus, even without offense on Shuffle or BC or BetCoin or DuckDice or other casino who share same provider, the "presumption" [or rather... judgment] will eventually fall to "darkness" and "UID 12345678" in form of either ban-hammer or being limited.
Makes sense, but they should make it clear to the gamblers in question instead of asking them to specify their other accounts. This is usually how arbers get caught across sportsbooks with a common provider.
And about who to believe, I tend to approach cases with believing no side. I approach cases by questioning the sincerity of both sides. Thus I ask for the narrative from both.
Have observed this neutral side of you for a long time now in various situations and cases which is why I feel that you are quite possibly the best mediatior between casinos and gamblers in this forum currently.