Your customer can make an offer at a lower (or I suppose, higher) price than the asking.
Your customer cannot change the shipping price. He can, of course, make an offer that effectively is a Free Shipping price.
For example, you have an item at $10 with $5 shipping. That's a total of $15. The customer can make an offer of $5 which with the $5 shipping makes $10.
He can't make an offer of $10 with Free Shipping. Or an offer of $5 with Free Shipping.
Some will, but technically.....
And it's actually logical, since often part of the shipping cost is already in the asking price. And of course, shipping is not related to value but to dimensions, weight and distance travelled.
