@Sonny209 

"what if in future i don't get invoice and have to refund them , would i be writing a check and choosing other current liability account to pay out of it ?"

You got it.  Assign the liability account to the check and you're all set.

"or if i do get invoice how would i apply"

You can move it back to A/R with a journal entry - debit the liability account, credit A/R.  Then apply it to the invoice using New > Receive payment.  Or, you can create a 'Customer Deposit' service product (select the liability account under the 'Income account' drop down in the product set-up screen) and add that to the invoice as a negative amount.  That will reduce the amount due by the amount of the deposit and reduce the liability account by the same amount.  Either way works.  It's up to you which one to use.