Selling a License? Legal?

This may seem like a weird one, but I downloaded the free trial of Adobe Captivate today and received an email minutes later someone offering to sell me their license.

"Are you looking to purchase a Captivate 8 license. I have a Captivate 8 license which I no longer use. I am willing to sell it at half of the price. Let me know if you are interested."

Is that legal?  How would that work?

Thanks for the help!