It's impossible for most pros to stay in decent "guest posing" shape all year round but the demand for special guests is always there 54 weeks a year.
Many times a Pro will accept a guest posing job with the understanding (or mis-understanding) that he or she will not be in top shape or even "anywhere near top shape". In some cases pros will accept guest-posing invites and appear on stage in some kind of costume that attempts to "hide" the obvious fact that he or she is totally out of shape and should not be guest posing in the first place.
I've seen guest posers appear on stage wearing gladiator type gear or simply plain old ripped sweatshirts and mainly concentrate on doing some kind of routine that he/she hoped would impress the audience somehow without revealing too much "fat" or lack of muscle.
In the old days and in some parts of the US that take bodybuilding seriously today, these guest posers would be booed off the stage. I've actually seen one guest poser being physically escorted off one stage for appearing fat, dumb and just plain stupid. But that was back in the day when fans and audience members were more outspoken regarding what and whom appeared on that posing dias. Back then complaints were taken seriously and usually settled immediately.
I've seen some promoters refuse to pay the agreed upon fee to top bodybuilders for appearing on stage as guest posers in less than the agreed upon physical condition of the guest.
My recommendation to any promoter is to promote a contest within a week (before/after) of a national contest and only invite those pros or potential pros who are dependable and, in fact, recommended by the NPC national office - if you need such recommendation.