In the episode Broke, Michael learns that his company's low prices are putting him out of business. He calls a client and asks for more money. Presumably, this is the same client that calls Dwight asking to come back. Dwight takes this information to Charles, but Jim intervenes making him look stupid, so Charles kicks him out.
Why didn't Charles followup on Dwight claim?
I know Dwight made Charles look stupid in previous episodes by making nonsensical suggestions.
He could have called the client and speak to them directly.
As David later points out, Michael's demands would end up costing Dunder Mifflin millions of dollars, so it would have been beneficial to call.