With Christmas in July coming up, I set up both Grumble Cave Monsters and Peaches and Pebbles' sales through Etsy on Sale. Instead of paying for each event, you purchase credits. The minimum number of credits you can buy are 10 - this is enough for two sales events - and you can link up all of your shops to one Etsy on Sale account.
Etsy on Sale is authorised by Etsy, and is fully respectable. Etsy on Sale will automatically change your prices by the percentage you have indicated, and will also add a prefix (such as ON SALE) to either your product descriptions or titles. It will also add a banner to the top of each product image indicating the original price, and then the new price beside it if you enable this option. Then, at the end of the sales event, it will put everything back to where you want it to be.
I used them before in 2012, and found them to be amazing. The products that are included in your sale are also displayed on the Etsy On Sale website, furthering exposure. Signing up is free, and you get a free 5 credits when you join - enough to run a sale event and use the tag-tool. But, if you sign up with this link and use the code IL6MS04M1G you can turn those 5 Etsy On Sale credits into 10!
Etsy On Sale is a really valuable tool for Etsy sellers when running promotions
and I highly recommend them.