Whenever a Realtor has a client that they represent, they are supposed to have the clients best interests in mind. You shouldn't be at risk letting your realtor know your motivations, expectations, and what you're willing to do in buying or selling a home.

Are things sometimes revealed when they should not have been? Yes, it does happen. For example, maybe you are willing to pay 5k more for a home than your original offer. You really want the house, but for the best price possible. What if your realtor relays to the seller's realtor that you have room to come up in price?

How would you prefer a Realtor handles the situation? You don't want the seller to just decline if they don't like your offer, so instead of offering information up the Realtor should say "Have the sellers send back what they feel is fair and I'll see what the buyers think." Do you see how that's loaded... the seller is basing price off feelings and the buyer is basing price off thinking.

What if a Realtor reveals motivation: divorce, health issues, financial trouble, etc.? If you're okay with that as a client it could be just fine, however you can see how information like this can be detrimental. Whenever we are asked why someone is selling a home, we simply say "They had a change in plans" as long as our clients are okay with it. 

Can you imagine being a buyer who is currently renting, and you need to close on a home by the end of next month because your lease is up? That's a little stressful, and how do you think negotiations would go if your realtor let the seller know that?

Make sure you've got a clear line of communication with your realtor to ensure they know what's okay and not okay. They work for you, and you're in control.