You have the possibility of transferring ongoing sales without bids to the seller account you wish to keep, thanks to the Club+ Gold.
You can then import them into the main account using the Easy Uploader tool.

To successfully transfer sales, all the accounts concerned must have a Club+ Gold membership.
FYI, the first 30 days are free when you sign up for the first time.

This article covers the following topics:

To subscribe to Club+Gold

If you are logged in to an account that does not yet have Club+ Gold, click here and select "Monthly payment" in the "Club+Gold" section. Then click "Start my free 1 month trial".

To export sales from the "secondary" account

You can export your ongoing sales in "Lister / Easy Uploader" format (it is important to export in this format).
This article explains how to proceed: How do I export my sales?

Warning: the exported file remains valid for 3 months. After that, the links to the images will expire.

To import sales to the "main" account

You can import the sales file previously obtained by using Easy Uploader.
This article explains how to proceed: Listing your items with EasyUploader