I'm not that familiar with Poseidon's service policy, but is it possible that if purchased from authorized dealers the original owner gets "parts for life"? And since you didn't purchase from an authorized dealer the "extra" they are quoting is for the parts?
Poseidons warranty is 2yrs so by the time it needs to be serviced the warranty is up, unless something goes wrong with it before then. Parts are not included for life like some other regulators are.
And since you didn't purchase from an authorized dealer
And I did purchase from an authorized dealer!!! that was listed on Poseidons web site. Just not my LDS
You have some good thoughts there WileEDiver