what is a good formula if any to go by when presenting to seller with profit margin included?
This is a standard rule of thumb. You should get comps to build a good ARV estimate. You should get a good estimate for the repairs that need to be made on the property to get that ARV. The price to your buyer should be (ARV * 70%) - Repairs. Then, you need to negotiate a price with the seller. Your assignment fee is the difference between the negotiated seller price and the buyer price. I think the biggest variable is the price negotiated with the seller, and you probably can't determine that before you negotiate. Of course, you need to pick a starting point and leave room for negotiations. That's a whole different topic and there are lots of books on that.
MR. Perkin Barry,
for your very speedy concise response, and I'm sorry for my very late, and much-appreciated reply, I've been going through a lot, plus this virus thing didn't help it any, you would've thought by me having to spend more time home and in I would've read and answered a lot of emails up here and elsewhere sorry again and thanks again.