If a product is sold out, then give the customer the option to receive an email when its available. On the product page display a field where the customer can enter their email address and submit.
Then when the product is back in stock, send a nice email to the customer notifying them that the product is available for purchase again, with a link to the product.
Optimally it would be great if webmasters can see which products customers are waiting on so that we know where we are missing sales.
We are currently using YITH Waitlist for this, but I'm certain that a Woodmart implementation would be better.