The thing about Salesforce is that it can take many forms. It is highly customizable. We have done a couple of integrations between Sage 100 and Salesforce because the existing integrations didn't quite do it. It seems, though, that if your customer is using the basic account/opportunity features, there should be a standard integration to do it. I haven't seen the Greytrix integration, but they've got a lot of experience in that area.