I would say don't waste your time... reason there are to many agents that don't understand the words "back up offer". If the property is listed with a real, on top of their game agent who understands and respects their fellow agents then yes.... you make ask what do you mean?? In today's market there are to many agents who don't know or understand those words. When their listing falls out of escrow, the first thing they do is put it back on the market, which is fine, if they don't have any "back up offers". See a real agent, one that has studied, learned and has respect for their fellow agents would pick up the phone ( which so many of today's agents don't do) and would call the other agents to see if their client was stil interested. .. hence the words " back up offer #1, back up offer #2 and so on.....if those agents who submitted the back up offer asked their clients and their clients said no.... then put the house back on the market.
I can say I have only had one client buy a house as a "back up offer" and that's because the agent called me and told me they were having issues.