I haven't bought through an OH but earlier this year we had 15 OH in an effort to sell ours.

I'd probably take down the posters. We were told to be as neutral as possible. For us that meant getting rid of anything police related obviously won't relate to you but you get the idea) and huge family photos.

Going against the grain a bit with the smells thing. While baking/coffee/food is great if you have a house that needs 'cozying', but in a newer house I think that freshness is the key. ie open the windows for a bit to let the air through and if you have to have a 'smell' go with what Bath suggested in a subtle vaporised oil. Overpowering smells make me suspicious of smoking and or pet smells, and as someone who doesn't smoke or have pets that would put us right off.

I would never go through someone's cupboards, but I am an organiser and cupboard space is important to me so I like to have a look at their depth. But that's just me.
You really can't pre-empt every person that could come through your house either, so I understand how tough it is.