I can't speak for what different postal clerks are doing. I would hope that all are following whatever guidelines that
Canada Post has passed along to them (I don't work for
Canada Post and have not seen any internal documentation about this matter).
From a consumer point of view, if I paid $1 I would expect a $1 stamp.
From
Canada Post's point of view, they (meaning the postal clerks) do not (or rather, I should say, should not) remove any single Permanent(tm) stamp from its full unit (i.e. from a booklet pane or roll).
[The only exception to this are the single stamps supplied in the Quarterly Pack and Annual Collections.]
Since
Canada Post's (and any other company) inventory system is most likely tied to the UPC barcodes and labels on their various products, I cannot see why a clerk would remove a single Permanent stamp from a roll/booklet and sell it for $1 when it only has a retail value of 85c?
Back in December when
Canada Post announced that rates were going up and that there would be different tiered pricing, my first thought was: I hope they come out with a "special" stamp to show the correct payment of $1 for a single letter ... and they did. One reason would certainly be for ease of use by the postal clerk but another reason would be for accounting purposes.
If a clerk is accepting $1 and only giving out a Permanent(tm) (85c) stamp then they should get some additional training.
By the way, from visiting numerous post offices (both Corporate and retail outlets in different stores) on various days (i.e. weekdays and weekends), there are all kinds of differently trained 'employees' out there. It is very easy to get different levels of service.