The contract typically provides that on failure of a vendor to deliver good and marketable title, the vendee (buyer) may rescind the contract and recover any deposit.
In general the vendee has to pay the tax.
The reward he demanded and received is for the article and the invention which it embodies and which his vendee is to practice upon it.
His position is thus that of a surety who is liable to his principal should the vendee make default.
It is a written instrument which evidences the transfer of title to personal property from the vendor, seller, to the vendee, buyer.
You cannot by legislation or by anything else do anything of the kind, or say whether a tax will fall upon the shoulders of the vendor or the vendee.
You can put the legal liability to pay the tax on the vendor or the vendee; economic law will work this out.
Would it not be desirable at the same time to see that the vendor does not transfer the burden to a vendee?