No, it is not possible for one column to be a foreign key to two different tables, although there is a workaround for it.
Create a "parent" table, which I'll call merchandise that contains basic information such as cost, department, availability, etc. that applies to all merchandise. Create two subordinate tables as goods and services which inherit their primary key from merchandise and provide more specific information.
When you want to sell something, you can sell merchandise (declare an FK to merchandies) without knowing or caring whether the item sold was goods or services!
In theory, theory and practice are identical. In practice, theory and practice are unrelated.