I have used this twice recently.
Officeworks beat a price from an online seller for printer toner by 5%. The cashier simply confirmed with a colleague that they were able to use the price from that particular seller.
Purchased a TV from the Good Guys, salesperson beat a competitor’s price after I showed details of a lower price advertised on the competitor’s website. I also found the same item advertised at a lower price a week or two after purchase and received a voucher for 120% of the difference to be used with 28 days. They do have limitations on which competitors they recognise for the post-purchase guarantee. The current conditions relating to the post-purchase guarantee are still very good but different to what is listed in the 2014 choice article.
I have also found some price guarantees to be worthless as different packaging or model numbers might be specific to the retailer offering the guarantee, making them different to an otherwise identical product being sold by a competitor.
When buying an appliance or other expensive item, I normally do a google search on the model number and a price comparison normally appears at or near the top of the results page. Whilst there is no guarantee that the lowest available price will be displayed, it allows for better negotiations when visiting with your preferred retailer.