First of congratulations on your sought after product. As a general remark I don't see any fundamental problem with dual licensing your product. You do need to

First of congratulations on your sought after product. As a general remark I don't see any fundamental problem with dual licensing your product. You do need to make sure that the license that you grant to the enterprise e-commerce company restricted so it does not permit the sale and marketing of a product that competes directly with your own but only the specialised e-commerce version. This type of white label product can be very lucrative and I think it is wise of you to go for a sales based license fee instead of a flat fee, especially if you are fairly confident that their product will be successful. Unless you have an opportunity to effectively address their market yourself it sounds like you are just optimising the income your product can generate.