The eBay policy is that offers are on the asking price only and do not affect the shipping price.
So if you have a $10 asking and a $5 shipping, the best offer could be $5 asking and $5shipping, but not $10 including shipping.
The result is of course the same,but many sellers use Calculated Shipping which varies with the destination and service chosen by the seller. And others use Free Shipping which really means a flat amount has been included in the asking price for shipping.
Make sure your customer understands this.
The bidder can ask that a faster or tracked service be used, which would raise the price. The seller is not required to provide this at the cost advertised by a slower or untracked service; she is entitled to cover her shipping cost.
A little negotiation.
The advertised shipping fee would be added automatically at checkout.
