What is the ruling if the seller alleges the buyer's claim of ignorance regarding the price is a stratagem to annul the pre-emption right?

Primary text

If the seller alleges that the buyer's claim of ignorance concerning the price was made as a trick (taḥayyul) specifically to nullify the right of pre-emption, the burden of proof lies with the buyer. The buyer must swear an oath to negate the seller's allegation of deceitful intent.