I've been on both sides, and the answer was always dependent on the customer, the tool, and the situation. As a (motorcycle) mechanic, I had customers ask to borrow simple tools for a few minutes, like a screwdriver to install a license plate. I had a customer ask to borrow my vacuum gauges overnight to sync his carbs. He offered a deposit, which I took, and returned them the next day. All understandable, and no problem for me.
But when I was asked for overnight loans of regular tools, like sockets and ratchets, I declined. Those are things I could not do my job without, and things that I would expect anyone with mechanical skills to own.
As a customer, I bought a transmission cooler from the Dodge dealership where I bought my truck. The parts guy said the installation required the use of a special tool to release the transmission fluid line from the radiator. This was a one-time deal for me. One of the mechanics at the dealership loaned me his, at the end of the day, to be returned in the morning. That was fantastic, and one of the reasons I stayed faithful to that dealership.