When I got my current car, it was 30 months old. The Ford dealer offered to Scotchguard the seats for me. I can't remember how much exactly, but it was a couple of hundred quid. I didn't get it done.

Is this a done thing nowadays, and is it worth it?

I've used the aerosol version myself, and it's crap and doesn't work.

I don't know what material modern seats are made of but they do seem to show up marks more easily than old seats.  Really noticeable in car ads, always wondered what people were doing to them.  Then I tried giving mine a clean with water and washing up liquid in the summer.  Once they dried they looked even worse, there are now watermarks everywhere!

The seats need to be perfectly clean before adding any coating, so I'd leave it to a proper vehicle detailer to clean and coat them.  It won't be cheap, but should mean it's done properly (unlike at car dealerships) and last many years.

If I bought one brand new, shall I just look locally for someone to do it then?