So we've all had this conversation (or variants of it);
"SOMEONE changed the customer type on this record! Yesterday they were a Customer, and today they are labeled as a Vendor!"
Basically, the problem is data control. How do we prevent these mistakes from happening? How do we track down the source of the error when it does happen? There two few fronts upon which to open our battle;
1. Prevent the mistake from happening by locking down (setting to Read-Only) critical fields. This is done on a per-field basis within each fields' Properties. Of course, this introduces considerations; the tighter something is locked down, the less useful it is (in general). Now, if someone needs to update the Customer Type field, they need to track down a GoldMine administrator (or someone allowed to make the change for them).
2. Log changes in History. This also is done on a per-field basis, also in Properties. The idea is that once you set "Log Changes in History", every time that field changes, you'll... get a History. Be careful though, this can "junk up" and bloat the History tab and make it less than informative.
Also, don't forget about the Summary Tab! It always shows the last update date and user.