When I was in the business it was just a flat no. And no explanation should be required, although we usually feel compelled to give one.
How's this "I can loan you the tool but I go with it and my time is worth money." Trailer is just a straight up no to all but my closest friends. I "gave" half interest in my good trailers to my best friend so I can say I only own half and we have an agreement to not loan it.
Or you might try the shame method, "Oh my god, you want to borrow my tools? How about my wife, want to "borrow" her too?
Only your very best friends would ever cross the line to ask and anyone else that stupid should just get a good trouncing for asking.
any of those answers help?