I used three different garages last year and no joy. Like some say, most are these new-fangled types that don't give continuous high flow.
But nevertheless, sometimes it's just the tyre + rim that's the problem IMHO. I found with one particular combo of tyres and rims that it simply wasn't going to happen so I gave up. Despite subsequently doing this for half a dozen rim / tyre combons successfully, when I went back to the original combo I'd tried last year I still couldn't make it work, and this time I got a bike shop compressor, wrapped the tyre round the middle, used every conceivable 'trick' and no joy. So I think sometimes it just ain't gonna happen (that was a rim strip option as they were Mavic rims).
Another set of (same type – 317's) Mavic rims and another set of the same tyres (Nobby Nics) did go up using Co2. No problem either !
Inexplicable. Same method used on both. One set took 15 minutes, another set took 3 weeks of trying on and off. And much frustration.
So for all the instructions on the site, given I follow them to the letter, and successfully make it work on some combos I think it's actually down to tyre + rim and whether there's some sort of incompatibility.
Personal view.