Most real estate offers require an inspection by a licensed exterminator to determine that the house doesn't have termites or other wood boring insects. The inspector will look for two signs in deciding whether or not to pass a house--an active termite infestation and evidence of a past infestation.
If your house does not pass the termite inspection, get a list of qualified exterminators from your real estate agent. Find out what treatment options they offer and what they charge for the service. Exterminators are usually quite competitive. If your home was treated for a past infestation, the company which performed the extermination may be willing to re-certify your home without a second treatment. Arrange for the termite inspection as early as possible, so you will have time to determine the best way to get rid of them, if they are found.