Trademark/Copyright infringement question.

I assume the question is whether you can be held liable for infringement. In each case, I assume that the use of the team logo is not permitted by the team or its league. In the first case, as long as the "customer" is the lawful owner of the decal and places the decal on the set for his own personal use -- not for resale -- there would be no trademark or copyright infringement. In the second case, if you lawfully acquire the decals and then apply them to your goods, without the permission of the league, you would infringe the league's trademark because the attachment of the league's mark would confuse consumers into believing that the sale was authorized or sponsored by the league (or team), which is not the case. On the other hand, if you merely apply the customer's lawfully acquired decal to the goods you have already sold to the customer, without suggesting, directly or indirectly, that the goods are authorized by the league, there would likely be no infringement, since the customer is privileged to affix the decals himself. Finally, under the third scenario, there would be no infringement as long as the customer is not confused into believing that the goods are authorized or sponsored by the league (or team). Remember that the first sale doctrine applies generally to copyright but not necessarily to trademark.