They are using WooCommerce. Based on how they have explained their ordering process previously, they most likely have it setup to hold stock for 80 minutes. This means if a bunch of people add items to their cart, it's going to hold stock and prevent others from ordering it. The actual inventory won't adjust until that hold time expires or the order is processed. If there's only 1 miner left in actual inventory, and someone pays before you do, you're simply out of luck because you didn't pay quick enough. They may also have WooCommerce configured to always show stock.

It's not a problem with their site. You just aren't quick enough. If you aren't on the site at the exact time they make them available and don't add to cart and checkout within a minute of release, chances are that you won't get one until held stock or another batch is released. I've been on the site at the exact times they've made them available and have been able to order just fine. First time I didn't even have to wait. Second time everything was gone in under a minute and I had to wait until held stock was released. Earlier batches sell out much faster. There's a lot of demand for miners, and everything everywhere, including used, has been selling out almost immediately. Check out eBay if you don't want to wait and don't mind paying 3-5x's more.

In the U.S. this isn't true. You're required to pay taxes based on the USD fair market value when you received or mined the coins. Even if you never spend or trade them, you still have to pay taxes. If you do ever spend or trade them, then you also have to report gains or losses based on the difference of value when received/mined and value when spent/traded. Being that there are multiple different exchanges with different Bitcoin to USD values, there will be multiple different ways one can determine fair market value, but you must apply it consistently.

For someone strictly mining, I'd think value could be determined based on whatever it costs to mine plus whatever profit you'd want in order to sell. Exchanges are driven by hype and manipulation when the true value of Bitcoin is whatever you want it to be until the government considers it legal tender or kills it off entirely.

Based on this, U.S. citizens are supposed to pay taxes on all virtual currencies.
https://www.irs.gov/pub/irs-drop/n-14-21.pdf

Seems like a giant can of worms when people can create any virtual currency they want and change the value of it at anytime. Is anyone really paying taxes and reporting gains/losses on Candy Crush and other in-app virtual currencies? Any app that offers in-app purchases for virtual currencies meets the government’s definition and you’re supposed to track gains or losses. If you buy some in-app “rubies” on sale, hold them,  and the developer marks up the price a week later, and you spend them, you owe taxes. Bitcoin only appears to be a target because of how large it is. How will they ever enforce the millions of other virtual currencies the laws apply to?

I live where they've been fracking for years and it's around $0.16 kWh for residential. Most of the gas is being liquified for export to higher paying countries where they have 20-year deals locked in.

I was able to get one from each batch on two different days. They sell out almost immediately but need to keep checking as they clear unconfirmed orders. Seems a bit odd that they keep releasing batches for the same ship dates and now the next batch says they will have ones that are in stock and ship out in 7 days. I wouldn't have ordered already if I knew that. Better practice would be to fulfill orders already placed. Instead they are probably just going to jack up the prices to see what people are willing to pay while making existing paid orders wait. By the time I actually get them I'll probably be selling them for something more efficient.

Don't even bother. CPU and GPU mining for Bitcoin has been dead since ASIC miners. I started with GPU mining in 2011 and quit in 2013 because it simply was no longer worth the effort. During that entire time I generated about 2.5 BTC through Slush Pool. This was with only two GPUs and I don't remember the specs but they were probably mining less than 10 Mh/s. You can only connect to Slush Pool with an ASIC miner now.

You could mine smaller cryptos with GPU. That card supposedly gets around 32 Mh/s. Most doing GPU mining for smaller cryptos are setting up rigs with multiple cards.