All years of 155 are pretty solid. 04 to early 06 valve issue is S/C motors only. Not common but happens. Once an S/C has been rebuilt, the ceramic washers are gone and are now steels.
Biggest single thing to avoid is one listed as 'supercharger just rebuilt, zero hours on new supercharger' etc. If a ceramic charger is rebuilt BEFORE it blows, no harm done period. But usually it's rebuilt after it lets go. It deposits ceramic sand and gravel in the engine. The owner goes to SeaDoo because the SC just went. SeaDoo tells them $1000 to rebuild SC and another $3k-$8k for the motor damage. Owner says 'just do the supercharger' and lists it immediately. You do not want this boat!