if there is a tear in the head gasket why does the mechanic take apart the whole engine annd is sending it off for a 150 dollar pressure test

honda 2003 lx just bought it used a couple of months ago and it drove fine and is
awsome to look st and i had inspected it before i bought it till engine light came on no
heating there was a gradual cooling loss and when the engine light came on the oil
looked dirty no other problems I stopped the car and when I checked the oil later it had
become sticky a bit coolant was green. I asked them 20 minutes after signing not to
start labor till i called next day again because I wanted to get back with dealer but they
had send engine already off. Dealer said car was fine and they should not have taken
the total engine apart and he could have done a 15 minute pressure test himself that i
am just doing a head gasket repair and not rebuilding an engine whom to believe tell
the honda people put it together again and get it repaired from dealer for less or beeing
cheated by the honda shop they want 660 dollar for this.They had already cheated on
me with my old honda 1996 it was in an accident mechanic told me 3000 dollar would
fix my car well it did not and whenever I drove that car there was lot of heat vibration
sound coming from the metall sheet. What shall I do I spent 9000 dollar on partly
buying the last car and repairing the other one it is terrible