I was given a sofa and it was absolutely filthy wasn't very clean - the ad (freecycle) said it was 'A bit grubby on the arms' - well - they weren't lying
I'd only got them second hand as I am renovating the house and simply wanted a couple that were clean and comfy that I wasn't worried about if they got a bit of paint on them or whatever - to be replaced when I've finished the work - so I didn't go and see them first or anything.
I stripped off all of the covers - read the washing instrustions on the base of the sofa.
I took it to the laundromat so it could go in two big machines (base cover in one, cushion covers in the other) rather than my smaller one - so it had lots of room to move around and get a good clean - I sprayed the life out of it with the pink stain removal stuff and shoved it in on a long, hot wash with lots of detergent (liquid), more stain remover and fabric conditioner.
Brought it all home - hung it on the line.
Came inside.
Read the small print (onthe label on the sofa)...
'Not all of our cover fabrics are suitable for washing - please check the label first'
OOoooopsss - but oh well, I was not paying for dry cleaning, I doubt it would have done the job anyway and it was NOT staying in my house how it was.... and actually, the base of the settee looks quite nice uncovered - but the cushions don't sadly or I'd have left them 'naked'!!
It dried on the line and went back on a dream. Clean.
Depends how much you are willing to risk it!!
Another hint is to put them back on when they're still a bit damp and stretch them out if you are worried. I thought I would wash them again if that was the case for me as I'd rather not have them on damp if avoidable.