Viewing a house three times and saying want to make an offer, even if offer is low, indicates interest. Most people interested in a house will view it a number of times. Usually first visit is quite brief - getting an overall feel for the house, checking out rooms, general condition of house, neighbourhood etc. Second viewing is where you look in more detail with a critical eye - trying to find out if the house requires any work, checking sizes of rooms, checking specific things which may have glanced at on first visit. Would usually bid after second visit.
Now, if I was interested in a house, and during second visit, I found that some part of the house is going to require work e.g. wiring, new windows, possible extension, roof etc. I would probably go back third time with a builder with a view to getting an outline quote and adjusting my proposed bid to take into account the cost of any work that needs to be done.
Its possible that you viewer is following a similar path, or else s/he could simply be indecisive.
I would encourage your EA to relay any proposed bids and circumstances of bidders even if bids are under your expectations. People are underbidding nowdays and first bid is usually under what they can afford. Encouraging bids and having your EA keep the communication channels open with both you and potential buyers may result in both you and the potential viewer finding a price you both can agree on.
