I've used Liquidation.com a lot over the past year, so here are my thoughts.
Steer away from sellers that do not have their merchandise in a liquidation.com warehouse. Some of those sellers appear to me to be the "fly by night" type.
I've had the best luck with the seller named "onlinereturns" which when you put two and two together, it's returned items (for the most part) from Amazon.com. A couple others worth noting would be "RetailWest1" and "PremierRetail". After working with them for a while (and sneaking in some conversation with an employee) you figure out which sellers deal more quality items.
I see some people saying steer away from "returns" but I give the green light on returns with dealing with the aforementioned sellers. But still note that 20-30% of the stuff will be screwed up. HOWEVER, I've still made some money from selling the screwed up stuff on eBay for parts.
Here's the trick on the screwed up stuff. Find out if your screwed up item is wanted for parts and then clearly stated and sell it AS-IS. If you have more than one messed up item, sell it in lots. The other thing you can do with the screwed up stuff is donate it to Goodwill, Salvation Army or whatever and take the tax write-off at full MSRP (at least in the US, not sure how that works in other countries). So even if 30% of your load is totally messed up, it's not a total loss if you know what to do with it. I've done a TON of transactions with these guys and only lost money on a couple lots (which you're going to get in this business if you do it long enough....don't get discouraged).
As far as shipping goes, I will agree, the minimum drives me crazy as well as the buyer premium. But that's part of the deal so do the math when bidding...and here's how that goes FYI:
Say I want to pay no more than $500 for the lot and the shipping quote given was the minimum of $40.25....
$500 (what I'll pay) - 40.25 (shipping) / Buyer premium (usually 8% when buying from a warehouse, so you actually divide by 1.08 to get the figure) = Amount to bid (in this case $425.69).
Back to shipping...Liquidation.com has worked for me because I am located somewhat close to the warehouse, so I can go pick up my stuff and not pay shipping. The flip side to that is you need your tax exemption in whatever state you pick up in to avoid sales tax.
And again....research the market you're selling the stuff in. Liquidation.com usually does a good job of manifesting the lots (especially the sellers I mentioned). So I sell on eBay and when looking for a Liquidation lot, I religiously research the items in eBay completed listings to figure out if it will be profitable and what my max bid should be.
Finally....Liquidation.com is an auction site, and auctions in general can become emotional! Don't get caught up in it, there will always be another lot. It all depends on who is bidding and who is getting caught up in the thrill of winning the auction (I would know, I've over-paid for lots just because I HAD to have it....dumb). My trick now, is to do my analysis, place my bid near the end of the auction then WALK AWAY from the computer.
Hope that sheds light into the wild world of liquidation.com!