@Nicola ******
I think you're actually talking about those b/s back door under the table volunteer visas that you get when you hand your passport and a pile of money to an agent/agency and they send it to a province you don't live in, use an immigration office you don't go to and get a 90 day Non-O and then a year extension for a foundation you can't pronounce let alone volunteer at for even one minute.
Don't get me wrong they are real stamps from real officers at real offices just not the one you use.
I just call a spade a spade and it is what it is. There's nothing wrong with going down the vlunteer visa route BUT you're going to go thru the agency to do 90 day reporting, and to cancel, renew or change it if you ever want to.
Prices run about 60K for the 3+12 volunteer visa (3 month Non-O and a year extension tacked on) giving you 15 months of trouble free stay