My wife and I gave up online orders for anything that was important.
If you're expecting dinner guests and so need four of something, or six of something, it really doesn't help at all to get your delivery only to find they didn't have six so sent five and one of something vaguely similar. At least if you go to the store yourself you can see they don't have six, so you can buy six of something else. It doesn't even work to say "no substitutions" because it just leaves you with five of something when you needed six, and unless you can group things together even an "all or nothing" doesn't work.
Sometimes they're really nice to you - they have an offer on multiples so you place an order to take them up on something like "three bottles of wine for a tenner", only to find they substituted one of the bottles for a more expensive one. So not only do you get to pay full price for two, because you didn't have a third, but the substitute costs more than you expected as well.