The idea behind price discrimination is that some customers will still buy the same product if it is offered at a higher price, while others will not. By figuring out which is which and offering them different prices, you can make more profit. For instance Uber is known to charge higher rates to customers with low phone battery, because they are probably more desperate and would be more willing to pay.

If a restaurant knows you have an expensive phone, they know you can probably afford more expensive meals and won't walk out if the prices are high. If you have a cheap phone, they might want to tone it down a little to avoid driving you away. They might be able to make more money by doing this.

Also you wouldn't need the waiter involved you can just check the user agent if all ordering has to be done through phones, the whole process would be automatic.

Wh… why would they do that?

If you've got a more expensive phone they'll charge more because they assume you have more money.

Alternatively, if you've got a cheaper phone they'll charge more so that they don't have to cater to the "wrong type of people."

I saw an article on lemmy about this yesterday, though not sure whether I'll find it again.

Hotels, flights, retailers already have an abundance of price discrimination. Target shows higher prices when your device is physically closer to a store and lower prices when you are further away. IPhone users tend to pay higher prices because they assume that since you had the extra money to pay for an expensive phone, you'll be open to spending more at other stores.

Likewise, if they see your device or other devices on your network/near you making several searches for hotels/flights the price will increase.

It's just another way to build greed into the system

In some places, the QR link redirects you to a page where you can order items without interacting with the staff.

While a valid point, it misses the possibility of people who may not know what useragent even means; it misses people who may not know that a website can identify what browser or device you are using.