We are probably in the vast minority of couples that are NOT looking for SFs (Unicorns), however we do know a number of SFs, all from LS parties. At a party, SFs get to see and interact with the Mrs as well as me.
In our case (much to the disappointment of a number of women), the Mrs has no interest in girl/girl play other than breasts, but if they had an interest in playing with me they can verify with the Mrs in person that it isn't an issue.
Since SFs are in such high demand, they likely have more online opportunities than couples and SMs, but there are other benefits to attending parties over online interaction. So many say one thing and then do another in person. At a party, what you see is what you get. There also tends to be less drama at parties because hosts will have people that start drama "fall off" the invite list.
For the SFs that I do play with in particular, they just have one more friend to watch their back for those very rare times something goes sideways at a party.

