Sintered is the most common base type and is better performing than Extruded bases.  A rental board may be Extruded.  I cannot remember if there are different tuning styles for the different base types.  I have always had Sintered and have tuned for that tho.  I imagine the repair shop would assume that as well.

from what i learned, sintered can not be added to easily. the guy that works on my board said they'll grind the base down to get gashes out, but if its really bad, they had to add another "sheet" because you cant add spots like you can with p-tex. sintered is harder to put huge gashes in than extruded, but when you put a very very deep one, the board is pretty much considered trash, because it costs too much to grind it that far down and build it back up again. thats why most people (other than pros, their boards are free) resist hitting jibs with a deck with sintered bases.
of course this is word of mouth, i take extreme care of my sintered board for this reason alone

Travz//, sound right but I think you have them reversed.  This is what I always believed:

Sintered is the most popular kind.  Is is softer and more porous and easier to repair.

Extruded is mainly found on rental boards and some park specific boards only for it's durability.  Harder surface, will not take wax as well and therefore slower.  Once trashed very hard to repair.

ref: http://en.wikipedia.org/wiki/Snowboard

frosty is correct by all information i can find as well. for some reason i was told never to ptex my
grudge because of the sintered base, it has to be ground. i dont know why, but its the info ive
stuck to. i dont now if forum bases are made a bit differently, but im afraid to try...

so this is where i get confused.
i was told never to p-tex my grudge which is sintered.
but i can p-tex the crap out of my manual and recon, which are
p-tex 4000 bases.

this is the info i got from forum, so i dont know what to think.
i know p-tex is another manufacturing process of sintered, i knew that before the
wikipedia guide, but since sintered is the melting down process of p-tex pellets,
and p-tex bases are compressed sheets of p-tex, i dont know what to do about scratches
in either now.

so seriously now im confused and worried so i need an explanation lol

Yeah, really hard to tell with the phone camera.  If you get just about any digital camera with a flash onto that it will be more distinct.

No biggie.  They might have just run a board with a black base over the belt grinder right before yours.  Might just be rub-off from that that got cooked in.

my board has the same thing happened to it. I hope I can get it off