Cleaning and servicing your HVAC system is annual maintenance. The furnace pictured has not been maintained annually. If it had been, there would be no rust at the burn chamber/burners, and there would be documentation of annual service calls on the furnace housing.
Most of the time if the furnace is clean on the interior, and there is no documentation of service on the furnace, it likely has been serviced. Usually the seller can get the records from the HVAC company who provided the service, if there are no visible service records.
In that case on the inspection report, it is noted as a “defect” of missing current service records. That “defect” in the summary of the report usually prompts the seller to obtain those records to present to the buyer, if the buyer and their agent have pursued that as a negotiating point. This is all for future home warranty purposes, in the event of a purchased home warranty by one of the two parties involved in the home transaction.
Sometimes I’ll hear “the warranty company wouldn’t fix or replace my furnace”, or I’ll hear “My air conditioner was working, and now it isn’t. It worked during the inspection, right?” Unless I’ve listed any components of the HVAC system as being inoperable at the time of the inspection, they worked when tested. But, during the testing of that equipment, HVAC service records are looked for. And if they aren’t there, the “Missing Current Service Records” defect gets put into the report.
Also, during the colder months of the year, air conditioners will not be tested and are stated as such on reports. Any time the temperatures drop below 65 degrees Fahrenheit, air conditioners should not be tested due to the potential damage testing the unit could result in.
This sounds like a ton of stuff to think about, but it’s really simple: get a home inspection!