When the summer season ends many things that used to be quite expensive before are often sold at lower prices so that people will buy them in autumn because otherwise all these clothes will be useless and they will be just thrown away. I'm interested to know which words you use to speak about such a fair where there are a lot cheap things on sale, for example, after the summer season.
The dictionary gives "sales", but this word doesn't indicate there are many goods on sale and they are much cheaper than usual because of being offered with discounts.
Your second sentence about grand summer sales would be unclear if there were no information about the fact that everything was cheaper there than usual. In orther words, you have to know something in advance or there should be hints and clues in the sentence. Right?
For example consider the sentence: "You'll manage to buy very cheap honey in a week when sales start in Gostiny Dvor on Nevsky Avenue". This sentence doesn't suggest anything about the prices there unless you know that there are annual cheap sales in Gostiny Dvor, the biggest department store in my city.
In the US, a "sale" at a store means the prices are lower. When something is ON sale, the price is lower. When something is FOR sale, it just means that you can buy it.
(By the way, I doubt very much that they just throw clothing away. That's what outlets are for.)
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
"Clearance" may be the word you are looking for. When a store has a clearance sale, they are trying to clear out the inventory, to make room for the new items.
I've edited your thread title because I don't want anybody to think there's a verb 'to sale', meaning 'to reduce the price of goods'.