Unfortunately if we set it too high , the effect on members security is usually the opposite ;(. I can turn it up to 5 a day , I realise that you have a large sale of about 20 items or so , so I am sure you can add them over a week . You might want to wait a week or so to make sure everyones happy , I always do
EDIT : It has security precautions in place for people that have a low iTrader rating so that they cant issue large amounts of feedback

Tell them to leave feedback for you first so you know they are happy , when you have a " few " up you shouldnt have a problem with returning them.