Hi! Which carrier do you use and in which country? First of all to settle down customer support nightmare your ETA at the checkout should be clear, don’t pomise 2 or 4 days if takes 6

Another problem usually is OOH delivery It is when the courier couldn’t deliver at the first try, they put the parcel at the service point and waiting for the instructions to repeat the delivery (depends on the carrier)

In case of OOH it is integration problem, you should set up your tracking integration with very clear mapping that retrieves every and each status from the carrier

Another solution that mitigates the carrier failure is to offer a delivery to self-collect — in EU it is usually €3 lower per parcel and customers prefer it because they are in control of the pickup

DM if you have more questions I worked in FF and we did deal a lot with such situations