IMO people who have actually met and spent time with the McCanns have a huge advantage over people who have never met them - especially when it comes to assessing the credibility of their actions/reactions and general behaviour.
IMO the opinions and conclusions of those people trained to observe - i.e. trauma counsellors like Alan Pike and the FLOs are far more reliable than the opinions of people who have never met them. Those people had the advantage of regularly witnessing the McCanns in private and out of the public eye.
Once again I refer to the Shannon Matthews case, where it was the FLO who first became suspicious of her mother because of her behaviour when in the privacy of her own home.
I very much doubt than anyone who believes in their innocence has come to that conclusion with no prior knowledge about the case - but purely on the strength of a meeting with them. That's simply not credible IMO.
AIMHO
Sir Paul Stephenson and Brian Kennedy decided they were innocent on the basis of one meeting with them. Jim Gamble appears to base his opinion on having met them and observed them with the twins.
Alan Pike's job was to help them to carry on, and the advice he gave them was suitable for bereavement or abduction because the effect on those left behind is very similar.
The McCanns dispensed with the services of the UK FLO's quite quickly. We don't know why, but Amaral says they asked uncomfortable questions.
Mostly people are offering their opinions. Whether their opinions are correct remains to be seen.