Microsoft has started offering a store credit of up to $650 for used MacBook Airs, with the credit to be used towards the purchase of a Surface Pro 3 tablet. The company hasn't specified what criteria is being used to decide on the amount of credit, only that it's "up to $650," and that the MacBook Air must turn on and not have display or water damage.

It's not that unusual for companies to offer a trade-in program on competing products, but in this case, Microsoft is offering a tablet in exchange for a notebook computer.

And it appears to be hoping you that won’t notice the huge price discrepancy of this "deal."

I took a look at the used MacBook Air market, and discovered that the oldest models of the MacBook Air are going for more than the maximum being offered by Microsoft. A late 2010 MacBook Air may be closer to $950, while a recent vintage model is going to be well over $1,000. One- or two-year-old MacBook Airs are commanding more on the used market than new Surface Pro 3s.

No matter how badly you may think you want a Microsoft Surface Pro 3, you're better off avoiding this "deal" and just paying cash. Then, if you decide the Surface Pro 3 is the greatest thing since sliced bread, you can sell that MacBook Air and make a pretty penny; possibly enough to pay for the tablet and have money left in your pocket.

Personally, I'm not a fan of tablets as replacements for notebooks, and that includes Apple's iPad lineup. Tablets have their place as content consumers, but they do rather poorly as platforms for creating content.