Something that I often do on the Daz sales pages is sort by % off. That will usually help highlight freebies, as well as illustrate where discount stacking might be particularly extreme. Usually, though, discount stacking is tied to new items, which is how the game is often played in the Daz store.
You need to have the Daz Deals plugin installed for the %off sort option apparently. If you spend ANY money in the Daz store, you really should get that plugin... info in the Commons section of the Daz forum.
A weak example of this is today's sale, where you need to buy 3 new items from today's sale to get a freebie, so over a $30 buy in for one 'free' item. So I wouldn't call that a good deal. Lately, I've adopted a '$2 average' rule, where if the average cost of all the items in my cart is much over $2 per item, I'll often just dump my cart. My Daz library is rather extensive at this point, so it's not a big deal for me to be 'choosy' this way.
Extreme examples of discount stacking used to happen a lot more often, with the cost of some items in the cart dropping below 10 cents in some cases, but the Daz sales team has been a LOT more careful about that within the last year or so. The 'plat club for a day' items sometimes are good deals, if the buy in isn't particularly steep, as those items are often priced much higher. But of course, those aren't freebies, so they aren't really relevant to the spirit of this thread.
I'm particularly annoyed that the Daz sales team has taken to doing the facebook offers thing. I'm not a fan of Facebook... so thanks for the heads up on the Grimes bundle!