Originally posted by Old n Slow
Had a nice surprise yesterday -- brought a boat over with two camels -- one demanded & one not. Delivered the demanded product (ALWAYS deliver demanded products first!) -- and checked before dropping off the second camel -- now IT was demanded! 
Saw another interesting sight -- again two camels on the boat. Dropped off the first -- gold -- and on the second look the city was now (gold), dye, silk. Dropped off the silk & the city became gold, dye (silk). I wonder what satiation adds to the question of effective demand changes.
The "flip" in demand you saw can actually be used to obtain limited control over the which items are demanded by a particular city.
First a bit of background.
I'm an inveterate freight builder and always start trading madly as soon as I have a basic RR network and transports in place so I can get the freight to market in one or two turns.
To maximize the return on delivering freight I never trade with a city, mine or enemy, located on the same landmass. A sea voyage of any length (1 square or 50) doubles the return.
Unless a good enemy city is within easy reach, I prefer to set up "trading cities", one as far north and the other as far south as I can find decent locations. These cities get rush city and terrain improvements so they grow fast (usually one of them becomes the SSC). All trade is directed to these cities. To maximize the distance bonus, freight from the southern hemisphere goes north while northern cities send theirs south. Also, before a freight enters its destination I rearrange its home city supply squares for maximum trade arrows and return them to normal after delivery.
The point of all this preamble is that as I have repeatedly monitored the long-term demand patterns for one or two cities I have observed two useful phenomena.
1. Assume that the following goods are demanded
uranium silk wool
Your transports have arrived with 3 uraniums (from cities U1, U2 and U3), 3 silks (from S1, S2 and S3) and a mess of freights with other commodities.
In some cases as soon as you deliver the freight from U3, the largest of the three U cities, the demand picture changes to
(uranium) silk wool
In this case, reset and try delivering U1 and U2 first, you may get a greater return before uranium is no longer demanded. Order of delivery does affect the demand. It generally pays to deliver cargo in ascending order of value. Anyway, as you make uranium deliveries, the demand will sooner or later become
(uranium) silk wool
At this point, start the silk delivery with the freight from S1, the smallest. If the the demand doesn't become
uranium (silk) wool
try delivering S2 and, if that doesn't do the trick, S3.
In most cases you will get a flip in U/S demand to
uranium (silk) wool
Resume U delivery. If demand flips again and you still have one or two S freights, it's time to start S deliveries again.
I have seen this toggling of two commodities work reliably for 20-25 turns but, like all good things, it eventually ends with
(uranium) (silk) (wool)
absolutely locked in place.
2. Using the above example but with no silk shipments, deliver uranium until it is no longer demanded and then start in on the assorted goods. Very occasionally these deliveries will bring uranium back into demand during the same turn like silk did. More likely, it will be in demand at the start of the next turn. Don't be too hasty in delivering your non-demand uranium.
This may be wishful thinking (it's nearly Christmas, after all) or just a gut feel on my part, but the greater the accumulated value of the miscellaneous shipments the sooner uranium seems to come back into demand, at least until the whole thing completely blocks.
