Here is my 3rd tips for fiverr seller.
"Read every details of each order. If you think you aren’t able to do any order then contact with your buyer as soon as possible and tell him about your limitation and send him a mutual cancellation. Remember, do not make delay in this issue. Because buyers may get angry for your late reply. Or may be he is in a commitment with others with this job and he may not accept your mutual cancellation because of his time limitation and commitment."