NOTE: POSTED THIS IS THE "S" FORUM, FIGURED IT WAS RELEVANT FOR M3 OWNERS, SO POSTING IT IN HERE TOO.
When my Dad bought his car last year, he wanted it with FSD for $8,000, which is what it was at the time. $5,000 for EAP and $3,000 more for FSD. That's what was agreed upon when the order for an inventory car was placed. The inventory car didn't have it, so it had to be added, which Tesla sent us an invoice that reflected the $3,000 price change as the inventory car originally only had EAP. Somehow, when he actually went and took delivery of the car, they didn't include it. After digging through old paperwork, he did pay $3,000 less than what the invoice price was. With Tesla, everything is done so quickly with most of it online, so my dad didn't catch it when he went in and signed the final paperwork to take delivery.
(EDIT - FROM THE FOLLOW UP POSTS, SOUNDS LIKE MY DAD JUST GOT LUCKY AS IT APPEARS TESLA HAS CHARGED MOST PEOPLE SALES TAX)
Discovered that he didn't have FSD doing a random check of his account. So, the above is for those that think they may have gotten it, to double check your account and make sure you actually do have it. Tesla is well known for somehow missing these things if you're adding any features to an existing inventory car. (Ludicrous mode was an issue on another car Inventory car we purchased).
Anyway, unfortunately we didn't catch it when the price was $2,000, but with the recent price reduction, he lucked out and we were able to pay the same $3,000 that he was originally supposed to be charged for it. There had been some arguments on the forums about whether Tesla would charge sales tax on a software update. If you purchased it with the car, it's part of the sale price and you are taxed on it. We purchased online from California and there was no sales tax added. Confirmed that the car now has it and the credit card was charged $3,000 even. So, he ended up saving about $270 on sales tax thanks to the mistake. Had we caught it a few months ago, he could have saved over $1,000 by getting it when it was $2,000, but that's life.