You can send your customer a Google Tag Manager script, and when they install that script, they will have no idea that our script is inside of it. Then, so long as you don’t call the list in their Email Marketing app “GetEmails”, they will have no idea that the contacts are coming from us.
Buy them for 25c from us, sell them for $1.00 to your client! AND get paid 20% commission on top of it.