Like the man said, electricity can be tricky and dangerous. The fuse or circuit breaker is in the system to protect your wiring. 12 gauge wire MUST have a 20 amp breaker or fuse to protect it. If you replace that 20 amp fuse with a 30 amp fuse the wire is the weak link in the system. The 12 gauge wire will melt in two and never "kick" the breaker. If you are "lucky" it will melt quickly. If you are not lucky it will melt slowly and be a long, red hot heating element behind your shop walls prompting a visit from your local fire department.
Flickering lights can be caused by a malfunctioning power tool or a loose connection somewhere between the outlet and the power line outside. It can take a pretty sharp electrician to hunt down that single loose screw.
I reject your reality and substitute my own.