I have a Razer Diamondback 3G mouse, whose buttons are very sturdy to click. They make a lot of noise and require a lot of pressure to be pressed.
I thought about disassembling it, which isn't a problem at all, but I have no idea what to do inside of it to make it click easier.
I think any mouse works on the same principle when it comes to the two main buttons, so this question could be related to any mouse.