Clothers

Oxfam is a charity - they do not pay for clothes ...

Also - unless you have very good quality expensive/designer clothes - you won't get paid for them ... Why not donate them to charity.

I can endorse Sarah's comment from my own experience of dealing with my late wife's clothes.
She had/I still have a range of expensive stuff but, because they are not almost new and with designer labels, second-hand dealers are not interested.
I gave most of her stuff to a woman's refuge via a social worker at our mutuelle but not her formal/evening wear.

Depending on what kind of clothes you have (they deal with "high-end fashion"), http://www.ohmydress.be/ might be an idea. You can find an article about this in the May 14 edition (Week 20) of Flanders Today, which is accessible in the archive at http://www.flanderstoday.eu/archive/2014. The article is on page 11. The article explains how it works (basically, you mail in your clothes or bring them to the Brussels office; they photograph them, upload on the site, take care of the selling, and then give you part of the sales price).