As you are selling privately, and you have not signed an exclusive authority with us, you are free to advertise where ever you please. We don't want to limit you or your campaign, so we have no problem with you listing in multiple places or with multiple companies.
On the other hand, if you have already signed an agreement with an agent, make sure you understand what that authority means. If you have signed an exclusive authority with them, this could mean you are unable to list with any other company for the duration of the agreement. If you have signed a non-exclusive authority, this usually allows you to list with multiple companies at once.
It is best to speak with your agent about this directly, as it is crucial that you are aware of your obligations and commitment to them prior to going any further with buyMyplace.