Do you just say in the listing that items may be out of stock and will take longer? If so that is unacceptable, you either list items as in stock or you have to list them as pre-order items, you cannot hedge your bets and hope buyers don't neg you if your items take longer to arrive because of your poor stock control.

As for chargebacks I presume you mean Paypal claims, chargebacks which are done through a card providers bank are a rare occurrence, it is very easy to counteract, you either use registered letter, click and send, red satchel with signature required or eparcel so you are covered or if your items are cheap and it isn't worth spending the extra you build a small amount into the sale price of each item to cover the occasional item not received claim just as B&M stores up the price of items to cover shoplifting and damage caused by customers trawling through their goods.