This is very interesting of course but it is not the kind of hard evidence that you can use in court particularly and certainly not the kind of hard evidence which would make Argos put their hands up in order to avoid a legal action.
I think your position here is to gather as much information as possible and then if you feel that you are prepared to bring a small claim in the County Court, you should send them a letter of claim giving them 14 days to reimburse you money or else you will sue. On day 15, issue the claim. Don't bluff. Only make the threat if you are prepared to carry it out.
Unfortunately the newspaper article – which is helpful – is dated 2014. The case on this forum which I referred you to is later than that and that will be helpful to you as well. As I have said, you should look around the Internet and see if you can find other people complaining about the same kind of thing. Have you done this yet?
You could also read our customer services guide and then call them and engage them in conversation where you suggest that they must be fairly familiar with this kind of complaint – and if you're lucky a customer services person will make an unguarded comment that this is certainly true.
This kind of evidence will help you.
Although what you're saying is completely credible – your problem is to persuade a judge. For 600 quid Argus might decide to make a go of it and in which case I would reckon your chances of success at about 75% which is okay – but I normally prefer higher odds when I recommend people to take a legal action.
The risk for you is that you could lose your 600 quid, the claim fee, the hearing fee – and possibly the reasonable costs of travel if Argos decided to send somebody out.
The risk for Argos is that they will get a professional to do this so they will incur a load of costs which they won't be able to recover under the small claims rules and of course they risk losing. Only Argos will know the extent of this kind of fraud problem within their ranks – and it is unlikely that you will ever find out how bad that problem is. If they turned up in court then clearly you would ask them whether they are familiar with this kind of fraud – because you know the answer would be "yes". It would then be nice to ask them how many times a week to they get this kind of incident – but the problem is that you don't know the answer so it could be risky to ask them. The general rule is that you only ask questions that you know the answer to already. If they were to respond that they only get this kind of thing once a year then it would be very unhelpful to your case.
On the other hand, the only other explanation is that you have substituted the vacuum cleaners and you are trying to steal from them. This would be a serious thing for Argos to be suggesting. In a court case in front of the judge I would certainly ask Argos if they were suggesting that you were attempting to steal £600 from them. I can imagine they would be reluctant to answer and it wouldn't be worth pressing the question – but the point would be made in front of the judge.
I think you are going to have to make a personal assessment of the pros and cons of bringing an action. I'm sure these frauds go on and of course it would be very nice to see Argos taken down on this and the story published on this forum and also over social media and to your local press. You could make it clear to Argos that if they force you to bring a legal action then when you get your judgement – as you surely will – that you will make sure that the story is published in the papers.
This is an additional risk factor for Argos and they might prefer to settle.