Since then I've found out that, "In Stock. Ready for dispatch.", doesn't necessarily mean they have an item in stock. What it really means is that they think they may be able to source an item from a supplier. In the mean time they keep you waiting with zero communication or order updates.
Having worked in the book industry for a number of years, in a number of different capacities, I can say that this is now, for better or for worse, standard practice among online booksellers, including those with a physical bricks & mortar store. This includes reputable firms, most of which struggle to compete with these kinds of tactics and have had no choice but to adopt them or face closing down. That is the sad reality of the bookselling business nowadays.
The reason why some of these online sellers (of which Book Depository is the classic example) are able to sell the books much more cheaply than the old-school competition is precisely because they have few of the overheads usually associated with the book trade: no warehouse, no stock, few employees, just an online catalogue of books available from wholesalers, from which they fulfil the retail orders. That means a wait of a few days while their orders arrive, to be repackaged and sent out to the end customer.
And believe me, anything that can happen in between, can and does happen: books sold out overnight, or gone out of print, boats held up by a storm, airports closed due to weather/strikes/regime change, in addition to the more usual event of the shops' line of credit being over-extended, and the delivery being held up as a result...
BD used to be cheap and rapid, then it was bought out by Amazon, and speed and service declined in consequence. My last order, less than a year ago, contained 3 books, only one of which arrived - eventually. I did get a partial refund, after the replacement copy was supposedly sent out, but as I said, it was my *last* order.
I understand how frustrating it can be waiting without knowing what is going on. So I would advise readers to check out the sellers' feedback, buy from reputable sellers, support local businesses where possible, and to be aware of these issues and develop a little understanding and patience - not all delays are due to scammers or shady business practices - they are just the way things are these days.