Here the clues are obvious. Contractor’s tape around the boiler essentially condemning it.
It’s usually not so obvious. Unless the vendor has satisfactory recent documentation showing the heating has been recently serviced, always, always, always insist it is serviced by a reputable fully qualified heating engineer before you commit to your purchase.
It could save you money and will give you peace of mind.
Note here, also, the asbestos cement flue pipe. That’s another story!