A customer rebate accrues amounts based on whatever criteria you want to set up. For example, you can tell a customer that you will rebate them $5 for every item, group of item, or all items, sold between a specific time frame. As sales accumulate, amounts will accrue in an expense account and also in a liability account. When you decide to "pay" the rebate, you can go to Settle transactions and call up the rebate program and either give them a credit or transfer it to accounts payable to cut them a check.
A trade allowance has virtually the same capabilities along with several more. The trade allowances requires an allowance "fund" to be created, in essence a budget for how much promotion money is being allocated to the program. Trade allowances are also more for quarterly or monthly promotions in order to get the customer to sell more of a particular product or products. For example, one condition could be for food products that the customer put the product in their weekly ad and then put it on an end cap for display. They might give a 20% off the total sales for a few weeks for that.
So really the only difference between the rebate and the allowance is the allowance requires a budget of sorts and the rebate does not. Also, in the trade allowance you cannot easily select All items if the rebate is based on all sales.
