Shipping Issues

Hi all I bought the software today after trialing it for a month, ive done quiet a few things since purchased including getting my site speed to 96 following some great guide on these forums but one thing I can t do.

I want to use the suppliers section so I know how to order from when my customers place an order but I dont want it to charge the customers shipping for each suppliers products.

Currently is joe bloggs buys a products for supplier a he is charged correctly $9.50

If he BVuys from supplier a and b he its charge 2 shipping and so on.

how do I change this, I also have a free shipping over 175 rule I would like to keep.

Thanks for any help