Legal Question in Real Estate Law in Maryland

Yes, there is tax on selling a home in Maryland. It is not called "sales tax" but rather three separate "transfer and recordation" taxes. At closing the title company will calculate the tax and collect it per the contract. Typically the buyer and seller will split this tax 50/50 although that may vary in the case of a first time homebuyer or if the parties agree otherwise by contract. A deed cannot be recorded until these taxes are paid.

You may be also asking about a different kind of tax called "capital gains" tax which may apply when someone sells an asset (like real estate) for more money than they bought it for. Whether or not such a tax applies (and the tax rate if it applies) depends on the specific circumstances, like how long the person lived in the property, what other income they have, so forth and so on. Your son would be well advised to consult with a tax professional after selling the home to ensure accurate reporting on income tax returns.