Have a look, but be prepared to say no if you think the guinea pig will be too much work for you. Don't let your health suffer because of getting a new pet though .
Is it the two or more guineas you're looking at? Gemma's right that guineas need a companion really, they're very sociable animals
Were your guineas long haired before? - sorry I can't remember what they looked like.
Are you happy with/have access to your local vets?
Have you got a vet fund ready & waiting -just in case the person wants to get rid of them to save him taking them to a vets for treatment?
(Try & find out his reason for wanting to get rid of them, check he's not just a breeder wanting to get rid of excess/ill stock, etc?)
I'm guessing you still have some of your old guinea pigs things, so that would save you buying new (if he really wants to get rid of them so badly & if you're having them, get him to put in food ,bedding, housing, hay ,etc for nothing or as little as possible too -if you need or want it.
Don't let him make any profit it sounds like you're going to be doing him a favour if you have them.
If I remember rightly it's you that's done the dog grooming course isn't it?
Sounds like a Peruvian hairstyle would be ideal for you to practice & perfect your grooming skills with
but they do need a lot of brushing, teasing out little knots/Matt's & summer bum trims so they don't get wet tangled & smelly hair.
Let us know how you get on & if you do take the plunge again....we'll need photos!