As a seller, you have the option to offer whatever delivery service you like. However, if you want to use couriers rather than AP, it would make sense to offer both services. That way people in city areas can use a courier if they like, and those of us in rural and regional areas can select AP. There are members of these forums whereby it's a 4+ hour round trip to go and collect a courier delivery from their depot. I would also suggest you mention in your listing that you offer both services. If you only offer courier, then definitely mention it so buyers like myself don't buy from you.

As a buyer, you have no choice apart from what the seller offers. If my sellers offer courier only, I hit the back button immediately.

Edited to add: I have only had 3 items go missing in transit and one parcel got stuck in a game of AP ping pong. Contacting them got the parcel out of the game and on its way. Overall I find them to be pretty good.