I ordered a gig on fiverr where i want a specific task to be done. That fiverr seller used a codecanyon plugin(regular license) to complete the required task in my website. I didn’t buy that plugin, so i’m afraid if accepting his work is illegal.
And you are probably right, especially if the price was low ;(
You can always ask for a purchase code. If he wouldn’t be able to provide you one, he probably uses one licence for couple of users (that’s definitely illegal ) or simply downloaded the files from some warez sites and it’s still a crime