First of all they do not sell SK EuroBonus points. I guess one issue is that Point transfers from one account to another are very expensive. It only makes sense for the couple of programs where point transfers are affordable. In the end somebody sells his points to the broker which will sell the points to you, so in the worst case two times a transfer fee.
Second, this is not allowed by most of the T&C of the programs and you are asking for account reviews doing so - in a lot of cases you will loose everything due to breach of the rules if they see this behavior.
Third, even if everything would workout you would only get Extra points, no basic points. You can only get basic points from flying, exchanging Extra points at a 15:1 ratio in the EuroBonus shop or buy Basic points in the EuroBonus shop.
Three rules I would always follow:
1) Never ever buy EB points anywhere else than the official EuriBonus shop
2) Do not sell your points to a miles broker
3) never but a dirt cheap business class reward ticket or airline miles from a miles broker