A commercial property can be for sale and to let at the same time, so each row carries
both the active sales and lettings profile where they exist. Units are summarised only
(count and size range) — call the units endpoint for the units themselves.

Sizes are always expressed in square feet, both in filters and in the returned
squareFeet values, regardless of the unit the property is stored in.
Use transactionType to narrow to sales or lettings; note this is the deal type,
not the portal a listing goes out on.