OK there is no laws that are put that makes selling social media accounts illegal , However when you create an instagram account you agree in the terms of services that you do not sell you instagram account, Thus the question is, Is violating terms of service illegal.

Despite terms of service (TOS) being a legal agreement between instagram and the user.it is of a minor violation too minor most sites and places i visited to check it is against the law states that it is not illegal. If the service provider fails to meet the terms of service there should be a compensation from the provider. For example warranties, which repairs or even replaces your product anew if the product fails before a period of time. Whereas when you violate the terms of services you can be given penalties from the producer of the service or the product, which can be reinforced by court.

references

https://www.buysellshoutouts.com/blog/legal-sell-instagram-accounts

https://www.quora.com/What-is-a-TOS-violation

https://gizmodo.com/5901339/its-not-a-crime-to-break-a-terms-of-service-agreement-so-keep-on-not-reading-them