How do native speakers of spanish pronounce "c" in gracias?

i have bought oxfords take off in spanish package and in the tapes they pronounced the c in gracias/centro/cigarro like "th"(as in thunder in english). But my friend who brought pimsleur's program said they pronounced "c" like "s" in those instants.I checked that out... show more i have bought oxfords take off in spanish package and in the tapes they pronounced the c in gracias/centro/cigarro like "th"(as in thunder in english).

But my friend who brought pimsleur's program said they pronounced "c" like "s" in those instants.I checked that out myself.

Can any native speaker elaborate on this? I suspect it is a regional variation but which belongs to where I don't have a clue.
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