I like to get to know each client and what they are hosting so I can make sure that nothing out of the ordinary occurs.

Always give the client the benefit of the doubt, even if it is a repeat issue. If you determine that you are getting tired of the SPAM complaints and find yourself spending a lot of time to serve this one customer, then make them a deal where it will benefit both sides (charge them per SPAM complaint). I have implemented this before and it worked like a charm (went from getting 20+ complaints a week to 1 or 2). Just need the right motivation!