Pretty much agree with everyone else above that says as long as you let the people know it's free online... then yeah, you should be able to charge if you choose to.
I know unless a friend asked me to do it (which... funny enough someone I know at a local retro game store asked if hacking the 3DS would make it play region free which... well, obvious answer for everyone here hahaha... and he said "he'd have to think about it) I'd probably charge some money for my time since I know it's a long process... after all did it for 3 3DSes, all being standard NEW 3DSes (one English, 2 Japanese with capture devices) and yeah, since I'm usually up at crazy hours of the night just laying around either playing on my 3DS or just browsing the net (it's 4:31 am here as I type this xD) I had the time to do an "all nighter" and set them up... but yeah, usually took 4-6 hours, I think the final 3DS was 4 hours while the first 2 were 6 because... kept running into certain small problems (failing the "safe" test on one of the sysupdaters, while trying another got it to work on the file checker for example) I think my first 3DS... the final processes were taking so long I was up till 7-8 am (felt like I was on the homestretch forever)
And this was probably a few weeks back, which only just signed up here a few days ago, didn't need any help since... as everyone on here says, just follow the guide step by step.
And yeah, also agreeing with a few people above... it IS like charging a service, heck my dad used to try to fix the plumbing in the house himself... but every time he "fixed" it... it usually screwed up a bit later. So finally after calling a plumber to fix one problem we had with my bath tub... (faucet was leaking) they were going to charge I think at first $250'ish to fix it. My dad said they were crazy and that "he'd just look up a guide on Youtube and do it himself for free" sound familiar? hahahaha
Either way... he was glad he haggled them down to $130 because... it was definitely worth the starting price (pretty much took all day, they broke something in the faucet, and had to replace it, etc. and still ended up only costing $130 after all that hassle)
So yeah, you COULD do it yourself which... the guide that is currently up is VERY simple to follow... or... well, if the person doesn't feel comfortable enough doing it themselves, if the person they are asking is wanting to charge them, up to them if they want to take the time to do it themselves or just pay someone $20-30 for the job.