
Flags from Britain
What a question. I can hear you saying “When you need to get rid of them” and that would be true if you are under time constraints. People who are moving need to get rid of things before they move. Executors need to wrap up estate requirements. People who are divorcing need to split things now.
Time constraints affects the amount of money you can expect to get for something. The buyer has the upper hand, so to speak. So, if you know you’re going to move, don’t wait until you’re ready to move to begin selling your goods. And yes, there are good and bad times to sell certain things. Let me explain.

Gold lustre teapot, creamer, sugar bowl, and bowl
Let’s say you just found out you’re getting visitors from overseas at Christmas and you intend to have a large gathering. Your table is from Ikea and you figure it’s time to buy something more upscale. You, as a consumer, are most likely to start looking in the fall for something suitable. That’s when you, as a seller should be selling your dining room suite. That goes for silver, china, crystal and linens – anything that involves entertaining is best sold at that time. You wouldn’t buy all your Christmas decorations in the summer, would you? Then why would you sell them in the summer?

Garden ornaments sell best in the spring
The same goes for anything having to do with gardening. Accessories and furniture are best sold in early spring.
If you have the luxury of time, follow the lead of the retail stores (albeit maybe not quite as early) and sell your things when people want to buy them – regardless of where or how you’ll be selling them.