Recently I found myself requiring an LCD wall-arm and after looking around for one in the shops, I was seduced by the saner prices on ebay (some shops can advertise smaller arms from £50-£80.
I purchased an arm on eBay through a trusted seller who claimed the product was made from a "super-strong" aluminium/ metal. What I actually found when I installed it was that it was made from cheaper aluminium/ alloy which bent, twisted then broke apart as soon as the joint nearest to the wall was tightened up moderately. I hate to think what would have happened if I had actually mounted the LCD before I had tightened the joints as I would likely be taking the seller to court to claim back the cost of my monitor as well as trying to get a refund on the poorly designed/ constructed arm. The problem being on eBay at the moment is that there are so many of exactly the same type/ design of this arm, possibly using the same materials, that could present a problem to a future purchaser.
In future I will opting for an LCD arm made from steel rather than alu as I don't think that the saving benefit in getting a cheaper LCD arm here makes up for the risk presented to the more-expensive LCD attached to it.