The new fees start May 1st. Everyone will be getting free listings, store and non-store. Great! Maybe you have a lot more free listings and are getting ready to list them all this May 1st.
Be careful! May is a 31 day month! A double listing month for 30 day durations that automatically relist using GTC or Automation rules to relist automatically Fixed price 30 days listings in eBay Selling Manager and Selling Manager Pro, eBay Blackthorne Pro or third party tools like Auctiva and inkFrog.
If you list May 1st fixed price with a 30 day duration using GTC (or automation tools for relisting Fixed Price 30 days), you will relist automatically on May 31st. So you will have a "double" listing month and you may have to pay if it relists May 31 if you have used up your free auctions.
For example, if you get a basic store with 150 free and list a lot on May 1st using GTC, remember they will relist and use up more of your 150 free in the month of May on the 31st. So you should stagger out your new GTC listings over the first 5 to 7 days at least so that they will not have a large number double relisting in the same months over the rest of this year.
Same applies to a Premium store with 500 free and an Anchor store with 2500 free. And to a non-store with 50 free. Be careful with using GTC with automatic renewal every 30 days or automation tools that will relist Fixed Price 30 days.
Here is a list of double listing months. First date is listing date you use this month, then when the double month will occur, then when it will happen again
May 1, May 31, then no double months for years (7 years ??)
May 2, Jul 1/31, then no double months for years
May 3, Aug 1/31, then no double months for years
May 4, Oct 1/31, then no double months for years
May 5, Dec 1/31, then no double months for years
May 6, Jan 1/31 2014, Mar 1/31 2014, then no double months for years
May 7, Jul 1/31 2014, then no double months for years
May 8, Aug 1/31 2014, then no double months for years
May 9, Oct 1/31 2014, then no double months for years
May 10, Dec 1/31 2014, then no double months for years
May 11, Jan 1/31 2015, Mar 1/31 2015, then no double months for years
May 12, Jul 1/31 2015, then no double months for years
May 13, Aug 1/31 2015, then no double months for years
May 14, Oct 1/31 2015, then no double months for years
May 15, Dec 1/31 2015, then no double months for years
If you already have GTC listings, then they should have a random distribution of the days in a month. So whenever a month has 31 days (Jan, Mar, May, Jul, Aug, Oct, Dec), on the 1st you will have listings that will renew on the 31st. Assuming random distribution of the day you listed with GTC, then you can have from 3% to 6% of your listing to double list each of those months with 31 days.
Now you cannot avoid double listing months using GTC but you can minimize their impact on your free listings by not listing a lot of GTC on one day of the month, especially in the first 5 days of the month. Stagger them out.
So be very careful not to list too many GTC on one day during the first 5 days because eventually you will have a double month within a year. May 6 is a bad date to start a GTC listing on because you will have 2 double listing months early next year.