I was working as an assistant or a home renovator.
They have to work on a tight budget for some of the homes, and once, they thought buying a second-hand quality air conditioner would save them money.
There was an online air conditioning provider selling close-to-new quality HVAC equipment, and there were comments from satisfied customers. They had a local a/c serviceman who worked with them in the renovations, so doing the HVAC installation was no trouble. However, the problem showed up when they decided to trust the equipment from the second-hand cooling industry shop. The online air conditioning company had good deals for multi-split air conditioning units, with a matching thermostat for each, and replacement parts, which they promised were clean and uncompromised. The only part we’d buy new was the filters to ensure the home’s air quality. We only wanted an excellent a/c that would work in the summer and winter without multiple air conditioning repair calls. The last condition for what we wanted was that it should not be older than five years because it was likely that routine HVAC maintenance would not be enough to keep it functional for a long. Long story short, when the air conditioning technician came to do the installation, he found that we had bought equipment that would give the homeowners trouble as soon as it was summer. The person who sold it refused to take it back, so we lost money that my bosses had to dig into their pockets to pay for the mistake. Whatever you do, try to save for new equipment unless you know more about air conditioning to understand what to check when making the purchase.