Well my comment for World Wide Brands would be a waste of money, but you have to bare in mind that they are essentially in competition to us here, so although I stand behind my opinion, perhaps others without a perceived agenda may be better to advise you on World Wide Brands.
Essentially World Wide Brands is a wholesale product resourcing directory just as SaleHoo is, however SaleHoo is far cheaper, better suppliers, much better forum where members openly express ideas and advice and far better customer support.
That's my opinion of course : )
The Police Auctions site is one that I have not been aware of. I always recommend auctions as great places to source products, but not online auctions so much because of the heavy traffic.
What tends to happen with online auction sites is that big numbers bidding usually drive the price up if anything. On site auction house are where you can unearth some real gems, and the fewer in number that attend, the better your chances of snaggling a bargain!
Regarding Liquidation.com, the sellers are independent and as I said, you will get some really up front sellers, but you also get the ones that play loose with the truth. Plenty will tell you they did good on some lots, and plenty will tell you to stay away.
It's a play it by ear situation in my opinion, not guaranteed of getting a good deal, but in with a realistic chance if you do your research.
You will actually find a lot of sellers on liquidation.com are buying direct from liquidators and breaking the loads down to sell there tom resellers. I used to deal in the liquidated market, and I had several customers buying large amounts of cosmetics mostly, then they would break those pallets into small 250 piece cartons, and aim them at resellers to push on sites such as ebay and so on.
So with that in mind, and depending on what sort of products you are interested in, I would suggest that you also perhaps consider looking at the source, liquidators themselves.
If you can't afford to buy in serious volume, then the deals you will get would most likely rival those that you will find on liquidation.com anyway.