Hello Sir,
I've heard that you and your gang are in need of some [materials,drugs or weapons]. I am willing to sell you a large amount of [materials,drugs or weapons] for the market rate which is [price here]. Normally, i only sell at the market rate but if you and your gang become regular buyers I will decrease the price from [price here] to [price here]. This will benefit you and your gang because you will be able to [do something here] cheaper.
Please reply soon.. I think these deals will be beneficial for the both of us.
[Contact details]
Your sincerely,
[your name]