Well, I cannot say that I had very bad experiences with Farnell. Their prices are not too good but otherwise it was ok.
On your #1, there is a solution and TME uses it. The moment you press 'buy' for one item, the displayed qty drops with the ordered amount, it becomes reserved for you. If you do not finish the order in a certain amount of time, usually until the next day, all items in cart are released.
#2, yes, that happens everywhere but usually with the last few items or reels. The item which was backordered in my case was a devboard and they had quite a few on stock, over 10-20 pcs.
Otoh I had with Digikey another situation some time ago, more specifically with their free shipping. I ordered something like 5k pcs of hammond plastic boxes, which of course qualified for free shipping. After I paid, I received a notice that the free shipping will be around 600 usd. I understand that a pack of 5k boxes can be quite heavy and huge compared with a reel with ICs having the same value, but nowhere on their terms and conditions was stated such situation. During further dialogues I asked them how can I estimate the shipping if a similar situation will arise. They said to place the order and see because it cannot be determined before.