Conditions attached to offers

I came across a situation this week where I inspected a property for a 2nd time and was told by the agent that they had received an offer significantly above the guide price range and the vendor was happy with the offer so I had a couple of hours to make a higher offer otherwise it was going to be sold. The agent told me a condition of the offer from the other party (a buyers advocate was involved) was that the exact amount of the offer would not revealed to other potential buyers. Just to be clear this is a large family home on a big block in one of the more sought after Melbourne suburbs.

I rang the agent back a few hours later and told him that any offer I made would not be in the range of the other offer so I was out. Obviously he knew I was interested if the other offer fell through for any reason.

Seems the house has been sold.

My question relates to the way you make such an offer with such a condition that it is not revealed to the other potential bidders, is this something that happens regularly in the high end market?? I would imagine a good working relationship between the buyers advocate and the agent would be helpful in making such an offer.

Anyone got any thoughts??