Most sofa damage doesn't happen overnight — it builds up until one day the seat won't hold its shape. Catching the early signs saves you from a full replacement.
Watch for a seat that sinks noticeably when you sit, springs you can feel through the cushion, a frame that creaks or wobbles, fabric that's frayed at the arms and seams, or foam that no longer bounces back. Any one of these means it's time for a check-up, not a full new sofa.
A professional inspection usually takes under 30 minutes and tells you exactly what's needed — sometimes it's just a foam or spring fix, far cheaper than buying new.