Do you know anyone that sells flights with miles?
 

I am trying to buy miles/flight with miles, in order to get a better deal.
Have anyone done this before?
Any hint, other than Ebay?

Rather risky. If the airline catches on that someone sold you a ticket with miles from their account they could deny you boarding and leave you stranded somewhere. Take a look at this thread where a flyer was denied boarding on a trip to Australia because the airline suspected fraud:
http://www.flyertalk.com/forum/unite...ket-fraud.html

And another intereresting one:
Consolidated "My MileagePlus Account is Being Audited" Thread [Merged]

it is not recommended....

Highly not recommended.

Selling awards violates the rules of every frequent flyer program. Airlines have departments with names like "revenue protection" whose only job is to catch violators. They're good at what they do. (If they didn't catch enough people to justify their cost, the airlines would get rid of them.) You're likely to find yourself somewhere with a choice of (a) staying there or (b) buying a full-fare ticket to get back. That could cost more than the original round trip would have.

Naturally, folks who want to sell you award tickets - on eBay or anywhere else - won't tell you this. Do not believe them. They want your money and are not particularly interested in what happens to you after they get it.

If it sounds too good to be true, it probably is.

Also note that the Airline's right to bar sales of miles has recently be affirmed via a Supreme Court rejection:
http://www.flyertalk.com/forum/ameri...-09-815-a.html

And, since nobody else said it,

Welcome to FT, Celiomartins!

As others have warned, this is not something that should be pursued.