Assuming both people have a normal dislike of bureaucracy, the equilibrium will likely be pure trust, or a selfie. Possibly of them actually getting the vaccine, or whatever paperwork they are given once vaccinated. Anyone so untrustworthy that you suspect they might have gone to significant effort to fake being vaccinated is not someone you want to socialize with anyway.
Assuming both people have a normal dislike of bureaucracy, the equilibrium will likely be pure trust, or a selfie. Possibly of them actually getting the vaccine, or whatever paperwork they are given once vaccinated. Anyone so untrustworthy that you suspect they might have gone to significant effort to fake being vaccinated is not someone you want to socialize with anyway.
I think that’s a fair prediction.