Will it affect my order completion rate if the buyer cancels his order?
Order completion rates will drop.
Yes either you or buyer if cancel the order it affects the order completion rate. In some cases you can contact CS to cancel order or contact them to show that the buyer either unintentionally placed order or buyer changed his/her mind in the very start to cancel order, or he/she does not need services. They will cancel the order with affecting your stats (This does not happen in all cases).
Useful information thanks
Yeah i think it will drop
Yes drop your order rate.