They are duty bound to get the best offer.
But, given you have a tennancy, (even if short) and by making an offer directly would be cutting out estate agents fees, and are in a position to proceed immediately with no property to sell in a chain, might be in this market, in the position to give the best offer.
A genuine offer of £85k on a £100k house is a better offer to someone who must sell the property, than say £90k from someone who is dependent on sales ect ect.
In the current market, a property might be on a while – the duty to get the best price and yet actually get one at all, are in considerable conflict. I sold some repo’s very cheaply in rhe last recession, yet could hand on heart say I did my best in the circumstances, ie where I was instructed to “sell” rather than simply “market” a property.