eBay has decided to phase out access to Parcel Select Ground labels, even though USPS has made no changes in their services or policies, and it's offered by all other online postage sellers including PayPal, endicia, stamps.com, etc. You can purchase Parcel Select Ground postage through PayPal at
www.PayPal.com/shipnow
But do compare prices before you do that. For Zones 1 - 4, the USPS online price for Priority Mail is literally 10 cents more than Parcel Select Ground, and for Zones 5 - 8 the difference is less than a dollar. If you're a TRS you get a 3% discount when purchasing Priority labels through eBay, which makes it cheaper than Parcel Select.
IMHO Parcel Select ground should only be offered when necessary such as for hazmat or Oversize packages (i.e., length-plus-girth above the Priority limit of 108 inches).
