At the moment my take on the lend situation is this,
Yes you can use my cab but not my head, end of conversation.
If they abuse your stuff, you abuse them!
Soon i am to be the proud owner of a Barefaced cab with a poweramp rack mount arrangement, as far as im concerned as soon as it all arrives it will be the end of my lending days.
I will be using my stuff exlusively and all the time reguardless of whinging promoters/other bassists.
You've got to look after yourself and your gear, other bands will take advantage of you if you let them,this is an unfortunate fact of life.
Some of the nicest people i know can and have been very disrespectful of other peoples equiptment, in the heat of battle with all the adrenaline of the gig pumping around things just tend to happen.
You can avoid your stuff getting stood/sat/jumped on/off of by not lending it.
I might be coming across as a bit of a dick about all this but it is possible to say no to people without offending them, you just have to be polite, its not rocket science.