Are selling the group in telegram? that is really worst I think. If you are admin for the group means you cannot sell that group to someone. There is no use of buying that. For example, if all the members leaving the group one by one what is the benefit of buying the group channel.
I hope it is waste of time to look the people want to buy it. If anyone open the project they can easily promote with the help of bountyhive or someone else in the forum.