when salesman say“来一个西瓜” to you,it means he want you to buy a watermelon. when you say“来一个西瓜” to salesman,it means you want to buy a watermelon. in some place,people will say"整一个西瓜"，it's has the same meaning as"来一个西瓜"。 hoping can help you.

I'll have a watermelon. 来个....or 来点儿... is just an informal and friendly way to express our purchasing intention.

When you want to buy a watermelon and you can say this sentence. 来 something means "I want something" during shopping.

Wow, thanks! That's so helpful!

"来一个西瓜" indicates that "I want to buy a watermelon". Instead of saying "我要买一个西瓜", "来一个西瓜" is more casual and vivid. Literally it means "Here comes a watermelon" as "来" means "come" origianlly. “多来几个吧” means you want to buy a few more. Hope it helps.🍉