The physical work can look identical from the stairs down: drywall, flooring, a bathroom. What actually separates the two is legal status. A finished basement needs no special permit beyond ordinary renovation permits, while a secondary suite needs egress windows, minimum ceiling height, fire separation from the main unit and a permit specific to that use.
The financial difference follows the legal one. A finished basement adds comfort and general living space, while a permitted secondary suite adds rentable income a lender can count toward mortgage qualifying, which a finished-but-not-legal basement cannot do no matter how nicely it is built. A home inspection, typically $400 to $600, checks the physical work but not the permit file.
Whether your specific basement is one or the other, or could become one from the other, is worth confirming before you price the house around it. Get your hand-reviewed valuation from Joel Dyck.