We have had several of these. This is where a customer goes to a convenience store or even another bank and cashes a check on his account and then comes to the bank where the account is housed and deposits the cash into his account. This raises the balance in the account to cover checks that hit that day and the check he cashes at the convenience store or other bank will clear in a day or two. Sometime the customer will tell the convenience store clerk not to run the check for several days.
In my opinion for this to work they should do this about every day.
Hope this helps.