Hello, I am offering you special Christmas sale and this sale is only once per YEAR! I am not like other selles who they have discount ten times per month :).
If you will buy RPG starter kit OR Action game kit on Asset store. You will just send me copy of that invoice and I will give you other pack for free!
This action will end 26th December!
Unfortunately not that good a sale to someone who already has one of your assets as I do (RPG starter kit) 
What if anything can you offer existing customers?
Good question :/.
I can give you huge discount for other kit if you are interested. Just send me PM or email.
Seems very fair. I’ll have to consider it as bought quite a few assets recently and should really stop spending and start using them so for now free bump in case anyone else wants to take advantage.
Bought the rpg kit, looks like a good deal. I forwarded you the invoice.