When you force close and reopen the app, your game syncs with TL servers. It's up to date and ready to play. As opposed to a game which has been running for a while or running in the background on your device while you use other apps. In this case the game may sync itself and you may see this as a chicken waddling across the screen and you may even see your game go back a few moments in time as it does this.
This is always worth bearing in mind if you ever are going to collect anything random like drops from pets or deliveries or loading train. You want the game to sync before you make the collection rather than after which could put your game back in time and mean you lose that valuable drop like a can of paint you have been waiting on. So it is good practice to force close your app before you begin to play.
The game itself is not designed for the type of trading between players that we have been doing in this thread. When you put an item up for sale it can immediately go into the newspaper and be sold within 10 seconds.
If you are a buyer who wants that lucky fish you need to be able to see it in your neighbour's shop within seconds before someone sees it in the newspaper and grabs it. Your best chance of seeing it is a freshly loaded game which is fully synced with TL servers. Hence the advice I give is always to force close the app before visiting your neighbour's farm to buy.
As a seller, when I know the buyer is ready, I post a message on my wall that I am about to sell, I put it up for sale, I close my shop box and immediately force close my app.
I then re-open my game about 30 seconds later and most times the buyer has been successful in getting the item.
All this force closing can be a pain but it is worthwhile. From experiments I have done trading between 2 accounts on 2 devices I would say without force closing there is a 30 to 40 % chance of the buyer getting the item.
When both account force close before starting and the seller force closes immediately after listing the item I would say there is a 90% chance of the buyer getting the item.
40% versus 90% chance.....I would say it is well worth taking the extra time to get the precious resources.
Hope that explains it and I have not confused you more