Anyone else just have their reputation just nose dive for no reason sometimes, like we're talking going from 80 to 0.
It's people leaving with desires unfulfilled.
It happened to me, got stuck in this odd kind of loop before I worked out what was going on.
'Tier 2' guests were leaving happy, all desires fulfilled, and the reputation was climbing to 80-90.
'Tier 3' guests were then turning up (because reputation was great), not getting all their desires met, and leaving unsatisfied. Leaving all as a group it was sending reputation dropping to around 20-30.
Weird part was, going by stats at the top I had enough of everything they needed (bathing, food, drink, stables, etc.), so why were they unhappy?
Finally worked out the issue was essentially layout. You need everything evenly spread out so that guests have everything they want within a short distance of their lodging. Even if things are nearby, you also need to make sure there's a road to them (guests spend a limited time in town and walking across grass is slow) and that they're well balanced. For example, if you've got a bathhouse surrounded by taverns, yeah, it's nice and close to each one, but it's going to be full so often most of your guests won't be able to use it.
All I needed to do was move stuff around, problem solved.