There are models like the DV line with dead screens that are not economical to repair and you can't warrant the usual fix (if you call that a fix.)

There's a bigger problem in that NEW laptops start at 199 bucks and these can outperform many older laptops. So be sure not to get caught in the "crunch."

There's pretty good money in basic service but insure yourself as all it takes is one client that you didn't have them sign a waiver that you are not and never responsible for their data to take you to court. There may be a business person that could do same as they may claim your slow repair cost them millions in lost sales. Get your waiver up front and don't touch their machine without them signing it.

As to business license, that varies with each city so I can't answer except if you are going to do this, you will do that.

Try some flat rate deals like new HDD for SATA machines at 99 bucks. The drive is under 50 for a new 500GB drive and you don't include installing the OS. Make that another charge and add services like ordering restore media. Plenty of services like that can keep you busy.

Protect yourself.