When an agent has dual agency they should represent each client fairly. First I would ask my agent to prepare a cma for you. This way you can see what has sold that is comparable in size and area. Second it would depend if there is any damage to the forclosure. Is it in good shape will it need many repairs?
Your agent will be able to explain the cma to you and help you with the offer.

The person to ask would be your buyer's agent...especially since it is his listing.

If you trust him to be your buyer's agent...you should trust him with selling you his listing.