Personally, I haven't met any property agents who dressed so horribly that it leaves a deep impression in my mind. I think a collared shirt (be it short or long sleeve) with long pants would seem presentable enough. Pretty standard. For ladies, perhaps smart casual office attire.
However, I have to disagree with Sheu Quen. Read this - http://quickbase.intuit.com/blog/2012/05/23/dress-code-or-not-what-you-wear-matters/
Sadly in the world today, how we dress DOES matter. If a person dresses sloppy and unpresentable, it might send a message across to others that they are lazy, untidy and ignorant. Even worse if you are a sales person or an agent trying to impress your clients with the intention to close a deal. If they really matter to you, I believe it's worth putting slightly more effort and care to what they wear to portray credibility and professionalism. Moreover, we can always wear what we want at home, off work or any other time of the day :)
Moreover, as the saying goes, first impression counts. If I have 2 agents standing before me, Agent A dresses up professionally and Agent B dresses up sloppy with t-shirt and shorts, without a doubt I would give my fullest attention towards Agent A with an assumption that Agent A might give me better advice and certainly seems more reliable and credible. This is called managing perception :)