S5 carbon build up

[cps13]

So I am looking at a 2008 S5 as my next car. After reading up a bit, it seems like cleaning carbon build up is "service" item as it is inevitable. The thing is, every person I have spoken to selling one, knows nothin about it, hasn't had it done and say their engine runs fine....or so they claim.

So my question is, is this actually a genuine problem that every S5 will suffer without fail, or is it being blown out of proportion?

Thanks