Numerous emails saying my shipping costs are too high

I sell a few items from home that are in larger boxes and weigh about 10 pounds. Shipping can range between $20-45 to send these items, so I put an average cost for the shipping and they are telling me it is too high and goes against their fair shipping policy.

So amazon can charge us 3X the cost to send in products, but we can't charge what it actually costs to ship a larger item to a customer ?