They are listing entities on their website and receiving remuneration for referrals therefore have a responsibility towards all customers that are arriving on the Best Change website only to be directed away when affiliate links are clicked. The danger was always going to be in the event any of those affiliated exchanges were to enforce a KYC/AML scenario on customers and if customers lost out financially who would actually be at fault.
Best Change have had accusation of their conduct raised in the past and I would still advise caution when using their website because once a customer has moved from the Best Change website to an affiliate exchange, it is the exchange that decides how to treat the customer: https://bitcointalksearch.org/topic/m.53617135
Ultimately, I think Best Change are partly responsible for any financial loss customers incur as a result of directing users to their affiliate websites. Those customers would not have been diverted to (and maybe never would have found) the affiliate exchanges had they not been listed on the Best Change website. As for the exchanges themselves, the very low rates of scam allegations against them (via Best Change) means thankfully this is still at very low levels. In the case you mentioned, why was the exchange not removed for their listing?
By them writing "Reliable and Trusted" on their website it does not relieve them of moral and ethical responsibilities towards customers. I wonder if any of those that are part of the Best Change signature campaign will look in to this and ask Best Change for an explanation.
The situation described then is similar to what OP is describing now. Made a payment to an exchange, the exchange then froze that deposit and demanded KYC. The exchange in question (although now inactive) is still listed on BestChange with a 100% positive rating and multiple "cancelled" claims.
But regardless of whether this is the first or the one hundredth time this has happened, BestChange need to do better. Their landing page says they only use "reliable and trusted" exchanges, and the exchanges are all "100% legal". They give exchanges a green tick to show they have undergone "additional checks". If this is true then BestChange should have, at a minimum, a name, address and company registration for OpenChange that they can provide to OP to let him take forward his claim, not to mention they should not be allowing exchanges to nullify all negative reviews with a single click.