Just got notified by Froogle.uk that we CANNOT use quantity discounted prices on their site (see this thread). I had the same conversation with PriceRunner, and they originally said no quantity discounted prices, and then finally said yes after seeing that all their advertisers were doing it. Moral of the story - be careful with the price comparisons on sites like Froogle, Pricerunner, Kelkoo, etc.
My slant on this? I trust Froogle more then the rest - I think their policy makes the most sense, and I trust that they will enforce the policy. In an ideal world, I think that BOTH the price for one item, and the lowest price per item in quantity should be listed. However, in the real world, I prefer Froogle.
My clients use price per one item in Froogle, and quantity discounted price on all the other feeds. The intention is NOT to deceive users - it's to show them where the cheapest price is. Additionally, it's to compete on a level playing field with those that are showing quantity discounted prices.