بعتُ
I sold.
اشتريتُ
I purchased.
Both expressions directly communicate a sale-related act. If the other conditions of a transaction are satisfied, there is no need to search for a hidden figurative sense merely to determine what act the words name.
Clarity of expression and validity of the full transaction must still be distinguished: ṣarīḥ determines the evident semantic act, while the legal validity of a contract may depend on further conditions.