Does a new smell, like pine, mean something was covered up?

Not necessarily, but a strong fragrance on an older car deserves a second visit. Ask when it was applied.

Should I bring someone else along?

A second person is helpful because your nose adapts. Ask them to describe the smell without prompting before you share your impression.

You may treat that as a reason to be cautious. Consider another vehicle or an independent inspection.

Not necessarily. Detailing can cover or reduce odor for a time, so test again under heat and with the fan running.

Yes. Bags, containers and spills can leave odor there, and it may be less masked than the front seats.

It may help if the filter is saturated, but seats, headliner and carpet can still hold odor, so retest after replacing it.

Cold smell first
Open the door of a car that has been closed for several hours and note the first impression before touching anything.
Stand outside, then return
Step away for five minutes and sit in the car again to reset your nose.
Run the fan, then the heat
Start with fan only on low, then warm air, and note any change. Heat releases stored odor.
Check recirculation
Toggle the recirculation and fresh-air settings and smell at the vents.
Inspect the trunk and spare area
Residue and bags can hide there, and odor may be stronger away from the front seats.

Has anyone smoked or vaped in this vehicle, and has it been cleaned or detailed?
When was the cabin air filter last replaced?
Is there a record of any odor complaint or cleaning fee charged to a previous renter?
May I test it on a warm afternoon and with the heat running?
May I have an independent mechanic or detailer look at it before I decide?

Does a new smell, like pine, mean something was covered up?: Not necessarily, but a strong fragrance on an older car deserves a second visit. Ask when it was applied.
Should I bring someone else along?: A second person is helpful because your nose adapts. Ask them to describe the smell without prompting before you share your impression.
What if the seller refuses a warm retest?: You may treat that as a reason to be cautious. Consider another vehicle or an independent inspection.
Does a recent detail clean mean the smell is gone?: Not necessarily. Detailing can cover or reduce odor for a time, so test again under heat and with the fan running.
Is the trunk worth checking?: Yes. Bags, containers and spills can leave odor there, and it may be less masked than the front seats.
Can a cabin filter alone fix the smell?: It may help if the filter is saturated, but seats, headliner and carpet can still hold odor, so retest after replacing it.

General information for the Denver area, not a quote or professional advice. In an emergency, call 911.