Here was my complete response. It got posted too soon.
My suggestion is to make a child table. One Property has Many offers.
Then it�s easy to see the whole history of the buying and selling type offers.
If you did that then you could make a summary field of the maximum record ID where the offer type was selling.
Then lookup that down to the offers table.
Then you could do a summary field of the maximum ovffer subject to the condition that the tape was selling and the record ID is equal to the record ID of the maximum selling offer record ID
And you could also do something similar for the most recent buying offer.
