No, it’s not common sense. If it’s a legitimate request like “I need a logo done” then they just might be a resellers.
There is nothing from common sense in posting requests if don’t want to buy anything. Even if someone will post a request without buying something it’s still never against any rules.
If you come to a store and ask sales professional to show you a vacuum cleaner but at the end reject to buy it. Is that illegal? Absolutely not. People can choose if they want to buy something or not or simply change their mind.
Example of common sense will be “you can’t take a picture from the internet that you didn’t design and try to resell it as yours”. That’s common sense. But “they posted request asking for the same service that they are providing and I think they are just trying to use 10 offers from other sellers” is not a common sense at all.
If they are posting something like “I sell logos, reach out to me” then it is against the rules.
I read it and clearly said that what you are describing looks more like reselling case.
If you mean something different then you need to check again what you wrote and if there is a language barrier from your side and if you were able to describe it correctly.