Open houses are either a lot of fun, or a complete pain in the backside, depending on your perspective. For every pro, there is a con. It's fun to go check out houses. It's a nightmare to prepare for. Open houses only sell 2 - 7% of all houses sold. Your house might sell. The weather is bad. The weather is too nice!
As a seller in central New York, yes, you should probably have some open houses. I say probably because they really don't work for all listings. It depends on your neighborhood, the property itself, and who your target buyer most likely is. If your property is a multi-unit in a high rental area and your most probable buyer is an investor, I really don't see how a Sunday public open house would benefit you much. But I'm also saying some open houses, not one every weekend. Advertising the same open house too frequently will quickly turn your house from a hot new listing to one buyers perceive as tired and/or overpriced, or the dreaded, "there must be something wrong with it". That is particularly true if the ad repeatedly states you are a motivated seller.
Yes, you have to clean the whole house, thoroughly, and make sure there aren't any pet or smoke odors . Yes, you should leave (and take Fido and Fifi with you), as your presence could make potential buyers feel uncomfortable. You definitely want buyers to feel comfortable in your house.
But buyers, by comfortable in the house, I am not saying it's okay for you to open dresser drawers or the refrigerator door! And be honest with the agent - if you're under an exclusive buyer agency agreement with another agent, say so. More often than not the agent sitting the open is not the listing agent. He or she is there to make new contacts, and with any luck, pick up some business. If your business isn't available, let him or her know, and try not to take all their attention away from other people who might be shopping around for a buyer's agent.
To be perfectly pessimistic, there are days I have thought that potential buyers should be required to attend "Open House Buyer's Etiquette" classes. I could run down a list of do's and don'ts, but it's so much easier to point out the simplest factor: treat the property, and the people in it, with respect and courtesy. I've had buyers verbally abuse other buyers, yell at another's kids, wet mud across white carpets, snoop through drawers.
Probably the toughest to deal with as an agent are the parents that don't parent. I'll make a long story short, and relate a two hour open house nightmare as briefly as possible. Children from hell. All right, I can expand on that. Inattentive parents, two young siblings, toys, especially a purple baton with streamers (well, not by the time the kids were done with it), pale yellow walls. 45 minute post open house clean up included vacuuming, scrubbing walls, replacing water in the fish tank, and resetting two bricks in the front walk. Then, I spent another 30 minutes calling to apologize to the other potential buyers who made the mistake of stopping by.
I was ready to scream. The kids had a ball (literally and figuratively!). See, it's all a matter of perspective.