(Fifth update.) I've been purchasing from Amazon fairly heavily for years, not because I think it's the best source for merchandise (although it often is) but because its gift cards are the reward of choice for my participation answering queries for helpowl.com [which I've also reviewed for SiteJabber].
1. Price. Prices are generally excellent, and some purchases are tax-free. Many items are "eligible for free shipping," meaning that Amazon will not charge for shipping such items if their total price in one order is $25 or more.
2. Return policy. Return policies are easy and quite generous, and with items shipped by Amazon the company pays for return shipping, or may even waive the need to return the item at all.
3. Promptness. Shipping is always prompt, even when free.
1. Support. I've now downgraded my star rating because of the increasingly terrible customer service. The good news is that phone support is usually, perhaps always, available. The bad news is the quality of that support:
(a) Thick accents by agents apparently based in other countries--even supervisors--make their advice largely unintelligible.
(b) Even when one can understand them, too many of the support personnel seem entirely clueless, taking the customer's time to no good end. Escalating to a supervisor sometimes works but often does not; and written support, usually provided as boilerplate, is usually still worse.
(c) Inquiries to Amazon's sellers must almost always be made via Amazon's online form; and, incredibly, Amazon cannot track such inquiries or follow up unless the purchase has already been made.
2. Product descriptions. These are wrong much too often.
3. Product search. The variety of products available is overwhelming, and Amazon's product search engine is awful. For example, a search for a "queen-size single fitted sheet" yielded many hundreds of results (as I recall, about 1,400!), pointing to sheets of various sizes, nearly all sheets sets. Of all those results I found only 1 that matched my search criteria. One suspects that Amazon deliberately fudges search results to offer more choices, with the goal of increasing sales.
4. Merchant reviews. As of last check Amazon allows reviewers without significant limitation to withdraw their reviews. This policy encourages merchants -- many of whom depend on Amazon for patronage -- to go after reviewers whose reviews are not favorable in order to buy them off. This has happened to me.
The consequence of these minuses is that you could easily spend hours trying to meet your need, which may in the end be unfulfilled or, even worse, fulfilled badly.