The charter companies all have their own internal requirements, but the ASA or other certificates are just part of what interests them. As mentioned earlier in the thread, the sailing resume is of much more importance. After this past week in the BVI (I'm at anchor
in the North Sound of Virgin Gorda at present) I can assure you that if you can answer the following question correctly you won't have any trouble:
Question: Which part of the sailboat is at the front when sailing or motoring?
a) Sugar Scoop(s) [end(s) closest to the steering wheel]
b) Pointy End(s) [end(s) furthest from the steering wheel]
In earnest, a sailing resume and the impression that the person doing the checkout with you gets from you, you will either have no issues at all or the charter company might put a temporary skipper aboard for a day. The rest is taken care of by your security deposit and credit card on file - the local disparaging term for bad charter guests is "Amex Captains".
I had my old boat at the Hodge's Creek SunSail base and my pastime was to sit at the Calamaya Restaurant overlooking the "A" and "B" departure docks. Along with the local dive crew we would sit, enjoy happy hour drinks and watch the antics - many charter boats didn't manage to even get out of the docks without trouble or scratches; all that was missing was the Benny Hill theme music playing in the background, or perhaps the Keystone Cops soundtrack.