Let sleeping dogs lie. How many things could you test for? Radon in the basement, for instance? I’d say put it on the market and if it doesn’t sell for a few months, reconsider. If someone likes the house, makes a good offer, and puts the condition on it that it be tested for EMF, maybe you agree to have it done—but make them pay for it.
Don’t test for it. The people concerned about it won’t really care what the readings are. They won’t want the house regardless. Make sure the realtor isn’t telling them in the future that they said you should get tests done.