You can deliver a product as fast and "good" as promised, but still loose a repeat customer. Here is a real life example.
Over the past days I ordered several books online. Usually, I use one specific company "A" (any guesses?) for two reasons. First, in Germany by law all German language books have to be sold for the list price, neither discounts nor coupons can be applied. "A" is offering free shipping on all books, regardless of their list price. Second, "A" is usually very quick in delivering the books and provides tracking information. I used this company as usual for some books.
Then, for an English book where every book seller can offer individual prices, I shopped around and found that I could save 2 EUR over at company "B". The product details showed that the book was in stock and would be sent the next day. I ordered the book in the evening and then started to wait for a confirmation email. And waited. The next morning I received 2 emails. The first was the acknowledgement of my order. The second was a status change email - now the book wasn't in stock anymore, but had a delivery time of 3 weeks. Ouch.
I checked the order status online and then the product page again. Both showed the 3 weeks for delivery. Why not cancel the order and shop somewhere else? I sent an email via contact form, tried to cancel online, and called the service hotline. On the phone they were friendly, confirmed the change to 3 weeks, wondered why it had changed over night and pointed out that it would be hard to cancel, but they would try anyway. The reason was they are working with a 3rd party fulfillment center. One day later, first the status said "trying to cancel", then it changed to "package sent", and in the afternoon the book arrived.
Company "B" delivered the product I ordered on time. However, their data isn't integrated and both customer and customer service are left to wonder about what is correct. Will I shop there again? Not this year... ;-)