Estate agents are in the business to sell a property so it is in their best interest to present you with a very tempting investment opportunity.
Some actually deal with letting so can also "advise you" of the potential rental valuation. Be cautious when dealing with estate agents. Over the years we have taken on properties for Landlords sold by estate agents who deal with letting who "promised" a certain rent only to fail in achieving it. We then take on the property and provide a realistic valuation and the property then lets. Quite obviously, an estate agent's interest is in achieving the sales fee.
Usually the excuse after the investor has potentially lost hundreds of pounds is "the market has changed and we need to reduce the rent" which is absolute rubbish as the property was over-valued in the first place.