Amazon's used conditions are more specific than eBay's, it also has special collectable conditions which you must get approval for.
The error you often get is that selecting a special, specific condition is not recognized by eBay - but picking the generic, used condition shows up on Amazon as "Used - Acceptable."
To resolve this, create a Custom User Field (what's that?) and map it to ConditionType in Amazon XML Mappings (what's that?). The acceptable values for this field must be typed identically to the way they appear here:
[New, UsedLikeNew, UsedVeryGood, UsedGood, UsedAcceptable, CollectibleLikeNew, CollectibleVeryGood, CollectibleGood, CollectibleAcceptable, Refurbished, Club]
Note: You must get approval to sell in the Collectible Conditions you can look up the approval process for your category in the Amazon Condition Guidelines.