Some things, it seems, never change. Like customers nicking glasses.
"The expert bar-hand sees that the glasses are clean and dry on the outside, before handing to a customer, and also that the counter top is kept dry and clean, as well as everything upon it. The beer service counter should be kept as clean as possible.
In a busy house it should be the sole duty of one or more persons to collect glasses, which are apt to be left anywhere and everywhere. Customers are frequently so absent-minded as to take them outside and put them in their pockets. I have known one hundred dozen to disappear in the course of a single week, from one house, in this way. Yet glass thieves are most difficult to detect."
"The Art and Practice of Innkeeping" by Alexander Francis Part, published by Heinemann London, 1922, pages 214 - 215.
During WW II, when glass was in short supply, losing glasses to theft was a real problem for publicans. They couldn't be easily replaced. Which is why you see what seem extremely petty court cases where people are prosecuted for stealing a couple of glasses from a pub.
The next problem for the publican wasn't from customers, but from dishonest staff.
"Even beers are not always what they seem, and the beer engine is a worthy ally of Ananias, when several classes of beer, at different prices, are on tap. Hence, some people consider that beer in bottle is of better quality than that in the cask.
Lest I be accused of lack of respect for "Beer, Beer, Glorious Beer," let me say at once that nothing can be of greater importance in the eyes of your Brewers, and customers, than the condition of your beers. I have known each, in their several ways, to show striking attention to it!
Silent reproaches, when accompanied by a decrease in receipts, are a mournful reminder that you may be the victim of some ghostly visitation which waters the beer. You may even be conscious of departing spirits, and yet find it difficult to lay the phantoms, which you can only do by collaring the cash, or the delinquent."
"The Art and Practice of Innkeeping" by Alexander Francis Part, published by Heinemann London, 1922, page 215.
I had to look up who Ananias was. A disciple of Jesus who dropped dead after lying about money. The implication is that a server could pull a cheaper beer than that ordered, charger the price of the expensive beer and pocket the difference. Could this be another reason for Mild turning darker? So that bar staff couldn't substitute Mild for Bitter?
With bottled beer, which has a label clearly saying what it contains, pulling a substitution would be much more difficult. Surely another reason the popularity of bottled beer was on the rise.
It's also implied that staff could be watering the beer. I'm not sure I see how that would work. Surely it would be the landlord who would profit from watered beer? I must be missing something here. Unless they wwere just drinking beer and then replacing it with water. I can see how this would work with spirits.