Help With Another New Zealand Stamp

I have an AR10, a Postal-Fiscal stamp.
It appears to be used, but there's a dark line along the entire left and right side of stamp, with a little bit of dark smudges on the front. To me the lines look smudgey, like dirt.
I think it would seem odd for a cancelation to run straight the entire length of both sides of the stamp, and then only have minimal dark spots on the front.
If it's possible it is some type of dirt, it could also explain, some of the dark marks on the front, (which then again, might just be a cancelation)
Is there a way to clean the stamp, to see if it is just dirt, or a cancelation.
Used the CV is $125.00, but mint, it's $525.00.
Thanks again for everyone's help.

The stamp is used, see cancellation.
The "line" as you call it, is the adjoining stamp impression, or part thereof, your stamp is the result of a mis-perforation.

The "dirt" is the beginning of foxing in the fine paper hairs of the separation.
Been in a humid environment.

Thanks.

And it looks like a fiscal/revenue cancel, sometimes done in pen, indelible pencil, colored handstamp or even an otherwise postal-looking cancel. A typical fiscal pen cancel is often like this with slashes separating parts of the date plus initials:

I think a date in pen is what I am seeing at left and lower left of your 8 shilling. This is fairly common used fiscally.

The high Scott price is for postally used stamps as these high values were uncommonly used that way.