The risk of getting stuck so hard on something metallic that you can't get the magnet off is extremely small. What's on the bottom is usually rusty and dirty, which significantly reduces the lifting power of the magnet.
In most cases, you will be able to pull the rope from different angles to try to "slip" the magnet away from the object.
The biggest culprits on the bottom are rocks and trees/branches. But even here you have to try pulling from different angles to try to get free.

No, unfortunately not, we have clear instructions in the product description that you should use some form of thread locking (type Loctite) in the threads when you screw the bolt and lifting eye together. And that the tightness of the air eye should be checked before each cast. Otherwise, there may be a risk that these will be unscrewed by vibrations/impacts from stones etc. on the bottom. This is also included in the terms and conditions that are accepted when purchasing from us.

Maintenance is actually very simple, dry/blow off the magnet properly after each magnet fishing trip and you will reduce the risk of it rusting. Rust will come sooner or later as the cup that the magnet is attached to is made of steel. Producing the magnets in a material that does not rust at all would cost far too much, resulting in even more expensive magnets for all magnet fishermen.
Also keep in mind that magnet fishing in saltwater speeds up the rusting process and requires even more care when cleaning.