I was interested in a property recently. Not overly interested,...

I was interested in a property recently. Not overly interested, but interested enough to consider an offer. The house has been for sale for nearly 2 years. First asking price was over 750k, and latest one was 599k. The house was huge and nice, in brisbane suburb. I wasn't sure about it because I feel that it's too big (6 br plus granny flat) for my small family. Anyway, I said to the agent that I'm considering to offer 540 cash settlement. He said he'll come and get us sign an offer letter, but he started to behave weirdly, such as saying there's another party, etc.etc, bank valuation is $650k, etc.
Now, before the signing went ahead, the house was withdrawn from sale. Just like that. I wasn't worry about it, until I saw on the oldlisting.com that it was then briefly advertised for $550k before it was withdrawn. I couldn't see it listed anywhere else, but then I saw those signs on the street, advertising this house as 'seller finance' sale. I contact the number on the board, and there's this weird reply inquiring too many details from me..I am puzzled with what's going on (I am first home buyer). I felt cheated by the agent, as I felt that if he was fair with us, the seller most probably agreed with what we were offering.
Is this normal in house hunting transaction, and what's the best thing to do to deal with it? I am just a bit annoyed with the whole thing.
Any other experience? Thanks