I'm one of the moderators and I'd allow it. I can't speak for the other moderators.
If a link is posted in here as an example to use for discussing IP law, I think it's perfectly legit. Posting an eBay listing to discuss the trademark implications of the listing is legit in my opinion.
Even posting a link to get people here to buy something is okay if the thing is related to IP law, maybe even just related to IP like tools for inventors. People have posted links to docketing systems, IP law support services, etc. That's all legit in my opinion.
Posting a link to get people to buy something that's unrelated to IP will get the post deleted and can get the poster banned (only if the poster is not a proper participant here). Making legit posts here protects you from being banned, so you're not in danger of that. In fact, you might even get an explanation why your post was deleted if you're a regular participant.