Its like this when it comes to credits being released
Your overall seller rating affects whether credits are held before the buyer marks it recieved or not.... So the higher and better your feedback is the more credits you can get before the buyer marks it recieved...
But then then the amount of auctions you have sold and no recieved a feedback for affect this to meaning if you have say 5 or more auctions open and are still waiting on feedback/marked as recieved from them you may find your credits being held again the better your feedback is the higher your limit is on this area.
Now the reason newbies get credits held at start is because they lack feedback to increese the limits we all start off with ^^