That is NOT a good strategy. You can start an auto number from a value other than 0, but you can not depend on Access to provide sequential numbers. Autonumbers in Access are meant only to be UNiQUE--NOT SEQUENTIAL. If, for any reason you removed/quit assignment etc, an autonumber could lose any sequencing you might "wrongly" depend on.
For Returns, you have a Date, a Customer, some Order Number etc, so you can match records based on those field values, and still use a separate autonumber as a key in your system.
Not everyone can access an accdb, you may reach a broader audience by attaching in mdb format.