Can I be personally on the hook for HST if my buyer and I get the going-concern election wrong?

Yes, and this is one of the more expensive mistakes a seller can make in a business sale. If the joint election turns out not to actually apply — because the deal didn't really meet the "all or substantially all" test, for example — HST is treated as having applied to the sale all along, as though no election had ever been filed. As the vendor, you are generally the party responsible for having collected and remitted that tax at the time of sale, so an invalid election can leave you facing a CRA assessment for the uncollected HST, plus interest, even though both you and the buyer assumed at the time that no tax was owing.

This risk sits with the seller in the first instance, which is why purchase agreements for deals relying on this election typically include specific protective language: a representation that the conditions for the election are met, and often an indemnity or gross-up clause requiring the buyer to pay any HST (and related costs) that turns out to be due if the election is later found invalid.

Confirming the sale genuinely meets the test before relying on the election, and documenting that assessment, is worth doing properly rather than treating the election as a formality.