Here's a copy of the letter that I sent to their customer services department:
Today I went to your store in Purley Way, where I bought a Chrome Tidy Rail (875/7049). I used one of your "Quick Pay" machines to pay for this, with my Argos storecard, and the receipt said that I should go to collection point A. This was at 15:58, and the estimated collection time was 16:01. So far, so good.
At 16:37, I was still waiting for my item to appear, and the store was closing. I then asked the person at the collection point about it, and he said that the boxes of this item were all on the store floor, so the item was never going to appear behind the counter. He took me over there, and explained that what I was supposed to do was pay for the item, then pick up the box and take it over to the collection point, where I could sign the receipt and give a copy to them. Apparently, if I'd paid for this at the checkout then the person on duty would have told me all this, but since I used the machine I was in the dark. I'm not quite sure what the plan would be if I'd paid at the machine with a chip-and-pin card; would I still need to take a receipt over to the collection point, or just pick up a box and walk out with it?
So, what could be improved here?
(1) Reprogram the machine to actually tell people about this policy.
(2) Improve your estimated pick-up times. Whenever I've seen them in the past, they've always been overly optimistic, i.e. I've always had to wait about 5-10 minutes after the estimated time before my item actually appeared. This meant that I didn't expect the item to be on time today, so it took me a while to realise that there was actually a specific problem, as opposed to general incompetence.
More generally, the reason that I waited so long was because the staff at the collection point were busy (serving other customers), and I was making an effort to be polite and reasonable, rather than interrupting other people to say "I demand my item now!" After all, it's not their fault if the people in the stock room are being slow, so I don't want to give them a hard time. But if the store had been open for another 4 hours (as it is mid-week), then the staff probably would have kept being busy, and I would have had a much longer wait. So, the lesson I've learned here is "Being polite means that I get terrible service - the only way to get good service is to be rude and bolshy". I doubt that this is really what you want, so I suggest that you do something about it.
Making things worse, I then got an error message when I tried to submit this at the website (the wonderfully generic "Sorry, we've found a problem with the data that has been entered"). After three failed attempts, I sent the message to firstname.lastname@example.org instead (to report the error), and hopefully they'll forward it on to the relevant people. All in all, this isn't exactly a triumph for good customer relations. Anyway, I'll post an update if I hear anything from them, otherwise they'll go into the forthcoming "Hall of Shame" section of my website (along with Overclockers and Amazon).