Transport, are you saying buyer has already paid for all seven individually?

Or that you have put up the price to include postage in each one, hence you now see them as overpriced, and can do a better deal due to combining?

You could offer to add in freebies as a reward for multiple purchases. Buyer is already happy to part with contracted $$, Any further negotaition is PR. Better to sell more or same $$ than sell same for less $$