I'm in the process of setting up a report/alert to review multiple customers using the same address. I was curious as to what others are reviewing, for example 4, 5, more or less customers using the same address.

The automated system we use will report (based on our rules) activity affecting the accounts of two or more primary (TIN) owners that have the same CIF address.

If you are able to use "fuzzy logic" to report on near matches, your reports could be more effective. That will cover the occasional typo and errors in input (street for road and vice versa, for example). You'll want to impose some sort of address standards; using the USPS standards is probably the optimal approach. That will give you standard abbreviations and eliminate virtually all punctuation (except hyphens, I believe).

This sort of report can also help identify private mailbox operations that you may not already be aware of.