I remember in a previous life learning something about customer service and a company's public image:
Over 80% of customers who have a poor customer service experience will tell their friends (ala Ditzyboy's post).
Only about 10% will relate good customer service experiences.
So you can see it's pretty difficult to get the "good" message across.
Personally, I reckon a new startup business (no matter what it is) should exercise some discretion for a period of time, in order to get people used to how it operates.
However, why should the 99% of customers that
do bother to follow checkin requirements and
do turn up on time be inconvenienced and delayed by the minority that don't?