I've learned two things about the webshops that sell Modchips.
First, modchips are a VERY hot product and it's hard for the resellers to keep them in stock. Often times the shipments received by the resellers are hardly enough to cover the orders on-hand. The simple solution, of course, is to buy larger lots but that becomes difficult when the manufacturers can't produce them fast enough to fill the demand. I've had experiences with a few shops now that just can't keep these things in stock. DMS seems to do a little better at meeting the demand but there's not much that a reseller can do when they're waiting on a shipment.
Secondly, these guys are often running an operation with less than half a dozen people total. They're handling upwards of 100 orders per day and often times things get mixed up. I had a bad experience with a reseller recently and was a very similar boat as yourself. What made the difference for me is how quickly they responded to my emails and made restitution for their errors (shipped via Priority when I paid for overnight). I was quickly transformed from an unhappy customer into one that would definitely buy from them again (The Console Corner FYI - thanks Steve!).
One thing I would like to see changed is how the resellers handle back ordered products. There are some out there that actually stop taking orders when they're out of stock - or even list the product on the website (or news section) as out of stock. It doesn't take much effort to keep customers informed and a simple email definitely helps customers rest a little easier.
I wouldn't base a judgement on one experience. The best thing to do is research in the webshop forums here and also check www.resellerratings.com ... with those two resources combined you should be able to find a reseller that you feel you can trust.
Best of luck and happy modding!