I am looking for a cross posting app that can create Ebay "bundle" listings. Like, one listing for A, one for B and one for both A&B. If A is sold, the A&B listing is automatically ended.
3D Sellers does this, but their cost is pretty high for someone who sells a small number of high value items. Also, they don't seem to have Shopify inventory syncing, except maybe through 3rd-party ad-ons.
