My house has been on the market with a realtor for almost 3 months and has not sold. The market here is slow I know. The realtor has had only 1 open house so far. I feel that is too little. Am I right to be concerned?
Not unless houses are usually sold through open houses in your area. Where I live open houses for the public are not very helpful in selling houses. To be blunt, they are mostly used by your real estate agent to try to find more clients. Nice for the agent, but not much help to you.
A realtor open house where agents (not the public) come to it can be helpful if the agents fill out a questionnaire and give feedback on the house. You have to take comments with a grain of salt but it can provide valuable feedback to you as a seller as to price, condition and so on. When we were selling our house it was the realtor feedback from that open house that told us we were overpriced -- despite telling our agent we wanting to price low.
In my area, Open Houses don't really bring in ready buyers. Instead they draw in neighbors and people who are just thinking about maybe buying. We did not do an open house for our house.
But now that we are shopping for a new house - I will say we are kinda of the exception in that we are ready buyers (preapproved for a mortgage) and we go to open houses. (Although neither of the two houses we've put offers on did we see through an open house.) It is just sometimes easier to do the open house than to arrange a time to see it with our agent.
If you really want to try an Open House, I think your agent should do that for you. If you haven't dropped your price recently, coordinating a price drop with an Open House might be helpful.