I try my best to avoid the sales person, usually by saying "I'm fine". Some are rather persistent and difficult to avoid especially those that turn up at the door stop. A good example is the Irish telecom provider Eircom. I think they called us 3 times in the past month and yesterday an Eircom sales person came to my house trying to push their packages.
For example, at the minute I'm paying â‚¬60 for my 5Mb Internet and phone with Digiweb and the Eircom sales person tried claiming their â‚¬50 package would be a better offer. I said I'm a new contract with Digiweb and he said some thing like "What a pity, as you could have been saved quite a lot by switching back". After a quick look on Eircom's website, I'm glad I did not go with salesman's offer - The promotional period ends after 6 months and goes up to â‚¬65/month and unlike my current provider, their package does not include UK minutes despite us regularly calling the UK.
Low cost items, e.g. <â‚¬20
For cheaper items such as under â‚¬20, it totally depends on what I'm purchasing and what the negative reviews are about (rather than the ratio of 4&5 star to 1&2 star).
A couple of examples:
â‚¬10 memory card - I'll generally avoid it if it has even a few negative reviews. I certainly don't like losing pictures, particularly in situations where you can't go back to take another picture. So even a very small number of negative reviews about card failures will usually put me off.
â‚¬10 ink cartridge set - Negative reviews about spilling ink, slow delivery or poor RMA generally don't put me off, but I do take them into account, e.g. being careful when removing the seal cap and allowing extra time for delivery. However, if the negative reviews are about terrible colour output, lines, etc. then I generally avoid.
â‚¬10 corded telephone - If I'm getting a spare, chances are that I'll just ignore the reviews altogether.
Medium priced products, e.g. ~â‚¬100
I tend to spend an hour checking through reviews, sometimes looking at professional reviews. For hard disks, this approach worked pretty well in my experience. I generally avoid hard disks with more than 1 in 10 negative reviews about DOA and failure, specifically on NewEgg and Amazon. The last 3.5" hard disk that failed on me was in 2004, despite purchasing ~20 hard disks for my two home PCs over that period. I sold off the smaller (<500GB) models later on. Before 2004, I had several hard disk failures as I was just buying them without checking any reviews.
Higher priced products, e.g. >â‚¬200
For more expensive products, I may spend hours reading reviews before actually forking out on it and I take both user and professional reviews into account. I generally skip reviews that don't look at real life use. E.g. a user review on a vacuum cleaner complaining about hose kinking, parts breaking and dust blooms while emptying says a lot more than a professional review boasting about its no loss of suction, manoeuvrability and low running costs. A good example would be the Dyson vacuum cleaner I bought a few years ago based on my real life experience with it. I've learned my lesson for not checking user reviews at the time - I now have a Henry.
In one case, I may actually look for negative reviews as to whether to actually by it. For example, if I purchase polo shirt, I specifically check if it's a slim fit size, which is rarely mentioned in the description. So if I see negative reviews about it being too small, then I'm fairly confident it's a slim fit size and usually this turns out to be the case once it arrives.
Finally, there are some products I will not buy online no matter how positive the reviews are. I can spend a good part of a day trying out shoes to find a pair that fits comfortably. If I tried out shoes online, I'm sure I would spend a good portion of a year returning one pair after another until I got a pair that fits.