How to avoid the joker mouth? Is it random or can it be prevented?

This should be avoidable by limiting the tightness of the suturing to achieve the lift and the preventing an overly upward vector of lift for any suturing which affects the corner of the mouth. With the deep plane lift there is excellent control of these variables and thes are some of the reasons I feel the deep plane lift achieves the best results. Best wishes, Dr. Donath

I'm familiar with the "joker face" result you describe. You can rest assured that modern approaches to facelift surgery are rather effective at avoiding this. In most cases, this look results from excessive pulling on the skin or the underlying muscles of the face. This causes the sides of the mouth to stretch to the point of looking unnatural or forced. The best way to avoid this is to choose a board-certified plastic surgeon with ample before-and-after photos to get a good sense of your potential results. Be sure to share your specific concerns with your surgeon for a better sense of how your particular procedure will avoid it. 

Prevent over-pulling the underlying SMAS, avoid too much tension on the skin layer, delicate handling of facial soft tissue, respect for facial planes and nerves within the surgical plane, awareness of the vectors of pull on each side, use of surgical landmarks/markings on the face to ensure symmetry; these are some basic core knowledge of a competent facelift surgeon.