I've found that borrowers fall into two completely separate camps - the same regardless of what you loan them, tools, books, money, ...
The really bad ones seem to confuse "loan" with "give". They keep things long after their need has passed, sometimes even forgetting they have the item or who loaned it to them. They don't take proper care of things (including their own), so when you finally get it back, it is not in the same condition as when you loaned it. I once had a person second-hand loan one of my tools to his neighbor When, after six months, I asked for it back, he said "Oh, Joe's got it. Here's his phone number" I found the (almost new when loaned) tool nearly bare of paint from scuffing, power cord insulation abraded through, trigger switch so packed full of sawdust he had been using it by unplugging. The original borrower didn't even take responsibility for retrieving it, let alone for fixing it!. Also, some folks have all the best intentions, but are simply inept. Then they act all embarrassed and back you into a corner where you are supposed to say "Oh, that's ok, don't worry about it".
A tough case is a professional with the attitude "wear and tear are part of the job; I don't have time or energy to baby my tools". One guy who watched me cutting stock with guide rail and TS55 told me "I'd bust that to pieces inside a week. Way too pretty and expensive to be of use to me". The TS55 is probably tougher than he realizes, but looking at his own tools he may still have been right. He just passes the replacement costs through to customers. So, should I loan him a tool? He'll probably replace it if he breaks it, but he won't think anything about minor damage and scuffing from what I would view as abuse.
The good ones treat your loan as an honor. They bring things back the instant they have completed a task. They show as much care for your item as you would. If they damage it, they fix or replace it. Another of my friends actually cleaned the rust off an old cruddy pipe wrench and reworked the mechanism so it functioned better. Another bought a new blade for my saw.
The problem is that until you loan something, it is very hard to tell which camp someone falls into. If they are one of the baddies, it is then too late. So, I allow only relatively inexpensive commonplace tools to go out of my direct supervision, things it is either nearly impossible to damage or I am due to replace anyway. My Festools definitely don't fit either of these categories!
Steve