As per Honda Service book, spark plugs has to be changed at 100,000kms (max). Not sure if previous owner changed them or not. Did they cleaned spark plugs during tuning? Try one test before purchasing new one:- Go to any good workshop and ask them to clean Spark Plugs, after cleaning all orange color should be gone and plugs should restore to original silver color. Ask them to ensure plug tip gap is accurate.
Then drive your car (on these cleaned plugs). If you feel difference in drive (light and responsive) then surely its your plugs. Buy new plugs, because if you kept running on these (cleaned) plugs then your drive will be heavy again after couple of days.
And oh before cleaning plugs, make sure your car has Original Honda OEM plugs. Might be previous owner changed them with after market (cheaper ones) 