For me, too messy is anything that can’t easily be fixed. So if guests spill red wine on a sofa, for instance, I expect them to tell me about it right away, and they generally do.
We tend to have the opposite problem and I specifically state in the house manual that we don’t expect guests to spend their last day cleaning. They nearly always do, particularly the French! I’ve also tried to make the apartment and the loft reasonably easy-maintenance and have had very little damage or mess that can’t be cleared.
Since we and our cleaning lady have perfected our routine, which consists of blitzing every available surface, I’d really just as soon have a bit of mess rather than something that looks superficially clean but not to our standards, so we’d have to clean it again anyway …
Also, because I like to keep an eye on things, we offer a “room refresh” every 4 or 5 days if guests are staying a week or longer. Guests always seem to like this, but they don’t realise it’s actually for my benefit so I can keep an abreast with any possible problems! So although I’m pretty much a Neat Freak myself, I’m much more laid back when it comes to messy guests.