The game doesn't factor in how well you do when shaving a beard, so you can cut a beard as poorly as you want and it will still count. Once you get a run successful enough to where you can AFK or idle and still be making money, then you can start rapidly trimming beards with one movement to rack up your beards shaved. It will still take awhile, but won't take nearly as long as actually trimming 10k beards. You can also do this while just watching Youtube or something else. Do not do too many though as you might start taking away too many customers to stay profitable. Also avoid doing it to high paying customers like VIP's, who are generally marked by having a yellow or green circle around them.

For a guide on how to setup a successful run, refer to this great guide, https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=809215916