Carpet cleaning - get professionals in or hire a machine?

[MrsJohnDeere]

In the context of getting upstairs carpets (and possibly one rug) cleaned before putting a house on the market?

It would depend on the price difference tbh

Are the machines you hire easy to use? Would prefer to go that route if they are?

Yes just like a weird vacuum cleaner

I have a steam mop, now don't laugh at my naivety but could I gently use this on certain particularly bad areas?

Yes you can - most come with a glider thing you put on the bottom but its not necessary to use - just makes it easier