Why can't one charge different prices for the same product? (Details Inside)

Well, you can. There are just limitations due to § 75–38 that you can’t in a emergency.

But Apple could totally spike the price of the new iPhone if they wanted. It isn’t illegal since there isn’t a disaster and it isn’t a necessity.

When I worked at Sears the prices went down as items stayed on the shelves unsold. The longer they sat the lower the price until they were finally marked down to a penny and thrown out.
Maybe I don’t understand your question?
Are you talking about bait and switch or false advertising?

@Judi It’s when lets say you have 20 washers and you sell them for $1000 each. Then you sell one and you re-adjust the price to $1025 and then you sell one. Then you adjust the price to $1050 because their all less available therefore more rare… then you sell one more and then change the price to $1075.
It was in one of my intro to economics text book in 1995.

There is nothing illegal about doing that but it just may not be a profitable strategy. Pricing can be effected by your inventory but its also effected by your competitions inventory.
I always mix up effect and affect. Someone tell me quick if I got it wrong!!

Perhaps where the book was written that violated some law, but except in cases of emergencies it would be legal here. In fact, if an item is flying off the shelves so fast you might not be able to restock before supply is gone, then you might consider taking it right up to $1100 to start. Price it high enough that you might have a couple left when new stock is due in. Then when new stock arrives, have a sale at the $1,000 that used to be the regular price. All legal and sensible business.

There are laws about fair trade pricing in the manufacturing and distribution of certain industries. For example, one part of Robinson-Patman mandates that products be offered to all customers in the wholesale trade at the same price. I can’t go into details on it, this was a long time ago for me and it was complicated.
There are also industry wide trade associations that set prices, there was a big lawsuit about almond growers being restrained from selling below a price set by a trade association. The price controls issue goes back at least 70 years to policies set in FDR“s first administration.

The government also sets price supports (price floors) that agricultural producers can not sell below.
The idea is to keep a marketplace competitive by preventing sales below cost on an industry wide basis.
Unfair, maybe but legal.

SRM