how can a buyer override my delivery costs

[aachaucer]

Can someone help with a delivery charge issue. My listings include a set delivery cost of £5.88, which buyers should pay. However, my buyer has selected their own which is a more expensive delivery option. This happened to me before and I was charged the additional cost.

What I don’t understand is how can a buyer override my set delivery costs of £5.88? Is it because the destination is in Northern Ireland?

[papso22 · Accepted solution]

Certain couriers charge extra to deliver to NI (RM don't).  If you chose one of those then the cost goes up, it is not something the buyer has done, just the result of where the buyer is..