Part 135 Captain reported writing up discrepancies for an airspeed split between Captain's and First Officer's airspeed indicators and for the First Officer's seat. Both items were signed off repeatedly without any additional repairs.

Narrative

The operator has 5-6 Aircraft X and Aircraft Y airplanes on its certificate. Crews operate on an X-on; Y-off rotation. The Aircraft X is very popular in the 135/fractional industry due to its low operating costs.Generally planes depart from a maintenance base by not always and are expected to operate for days on end without maintenance. Sometimes this works; but most times it doesn't.Write-ups on the road are discouraged and must be 'cleared' first with a call to Maintenance Control. This is a measure to manage contract maintenance and its associated costs.If deemed necessary; the airplane will be flown back to a maintenance base in its current state of repair. Sometimes crews are asked to 'live' with the issues; other times; contract maintenance is called in.Problems arise when maintenance issues become expensive. Attempts are made to correct the issue(s); but when a high-cost solution is the only option; progress grinds to a halt.The most recent example involves an airspeed split between the Captain's and FO's displays. Been a back and forth for several months. A test flight revealed a 3-knot split between the two displays. The manufacturer's guidance on airspeed splits is ±2 KIAS per display; for a total allowable difference of 4 knots. An argument ensued over the 3-knot discrepancy. Tests were conducted; the issue was signed off repeatedly; and the airplane was returned to service with crews told the situation was being 'monitored.' During the test flight; it was also discovered that the FO's seat was in very poor condition. The seat back and base exhibited excessive movement far beyond what is reasonable. Maintenance personnel inspected the seat and informed us that the hardware was worn out.We were instructed not to write up anything and assured that maintenance would handle it. The airplane was returned to service without any additional repairs.I eventually refused the airplane (which didn't make me popular); writing up the same two items: the airspeed split and the FO's seat. Both were immediately signed off; the airplane was returned to service; and a replacement Captain was called in.This is where another problem emerges. The majority of these Captains are young men and women building jet time to advance their careers. They have families to support; and the company is aware of this; using it as leverage to keep the fleet flying. Most Captains recognize that the aircraft were never designed to fly approximately 100 hours a month without an aggressive maintenance program. The aircraft simply aren't robust enough and were not built for that kind of schedule.I am certain this is not the only operator exploiting weak oversight in the FAR 135/fractional business. Compared to FAR 121 operators; these operators are getting away with murder.