Working for free opens a whole can of worms doesn't it. Just what constitutes working for free? I know a few Electricians and Plumbers and Carpenters that sometimes work for free. Usually this is through organisations like Lions,Rotary,Jaycees etc or could be by themselves by taking on maintenance duties for say Ronald McDonald house etc. This is charitable work or called "giving something back". One sparky I know belongs to a church and will fix members electrics if they are pensioners and can't afford to pay a contractor. Angel flight pilots also could be deemed working for free if they hold a CPL. Glider towing if a club member etc all is for free for the greater good.
This is a world away from offering to work for free at a business that is making money from your efforts. This is illegal and they can be prosecuted for it. Because you are not on their books you will not be covered by workcover. You are not a contractor either if there is not a record of payment to you as they can claim your charges off their taxable income. The tax office will also want your tax if a real contractor or employee. So we taxpayers are getting ripped off too.
Sometimes you read of unscrupulous small shopkeepers getting young jobseekers to work a few days for free as a "trial" only to let them go and repeat the process again and again. This is illegal. Do not partake in it no matter how hard it is to break into the workforce. Unfortunately there will always be some business owners only too willing to take advantage of the vulnerable. Report them if you have evidence as they not only screw their unpaid workers but businesses that do the right thing and compete against them.