Do they do the viewings or do they expect you to do them? I personally would not be prepared to pay anything more than an advertising fee to an agent who is unwilling to do the viewings as this is the main part of selling.
Also Saturdays are the most popular day for viewings. From your point of view, you want a prospective purchaser who calls up on Friday morning hoping for an appointment to see your house on Saturday to get to see the house, and for you not to be obliged to show them round yourself (best thing you can do to sell the house is to go out for the first viewings). So you could ask how does the agency cover Saturdays?
Which portals do they advertise in?
I know agencies would not agree with me, but there is only one pool of buyers per property type in each area, and people who want to buy tend to look on the portals (rightmove, primelocation, findaproperty etc), so they will see your house advertised whoever it is with. If they are interested, then they will ask the agent concerned for more details.
Do they take the photos themselves or do they hire professional photographers and floorplanners?
How long is the contract? How will the agency communicate who their buyers are if and when then contract finishes without the house being sold so there is no dispute should you appoint a new agent subsequently. The rule is that the agent who "introduces" the buyer is the one who gets the fee. However, you may feel that after 3 months, agent A has achieved nothing. So you terminate the contract and appoint agent B, who gets you an offer two weeks later. However, if the buyer was introduced to the property by agent A, then agent A will want the fee (and so will agent B). So you need to be clear about how this will work up front because contracts are for when things go wrong.