Generally, unit owners have to pay their condo fees even if they have a claim or dispute with the condo corporation.
If they do not pay, the corporation can register a certificate of lien against a unit. This lien can be enforced, if necessary, by selling a unit.
The sale of the severed portion of vacant land would not be subject to GST/HST since it is not capital property used primarily (more than 50%) in a business and it is not being sold in the course of a business. However, if the land was subdivided into more than two parts, sales of the severed portions are not exempt unless the portion is sold to a relative (or to a former spouse or common-law partner) for their personal use.