While this sounds anal, I think it reflects lack of confidence in how Sage 100 handles this. I don't think this doubt is unusual, and I think it arises from not understanding how the TB can be unbalanced. Given the skepticism, I'm surprised he isn't also trying to reconcile sales tax.
School him on how the system works, the relation between dates in subsidiary ledgers and GL. The things that are going cause problems are period straddles in invoicing and receipts, deposits, and GL entries made directly to AR, Help him develop a checklist to use with his Acctg Supv. Basically, when Sage processes are done correctly, it all works, so variances are people-driven.
Second option is for him to buy some custom reports from you to help put his mind at ease. Don't make them cheap, and don't guarantee they will always work, because our experience is that customers manage to find new ways to screw up things when not incented to learn the right ways first.