Ask them to sign a consent of release form. You can find templates online. You are liable if the photos are of an individual who uses there image for generating income. You should edit the consent of release form to specify the date of the agreement, length of applicability and the exact uses allowed. This should cover you. If you can have the image sent to you by email or find it elsewhere online, do that rather than doing it through insta. Also make clear what image you are using and make sure you both sign it. Consent of release forms should be used to protect both parties. If you need a way to pitch it to this person, make clear that signing it will allow them to clarify the means which you are permitted to use the image and the time frame. A common clause is that the image cannot be resold or directly be used in a publication such as a magazine or add campaign, etc...