Carryfast:
On that note the approaching retirement worker,not needing a big wage, still has to show just as much commitment to the job because he still has bills to pay too.If that wasn’t the case why would he bother.But agreed he is obviously, possibly rightly,seen as less of a desperate mug,by such exploitative vindictive employers because his outgoings aren’t perceived as being as onerous.
Agreed. On any reckoning, a man needing to work only part-time is more comfortable than the man needing to work full-time.
It may be that the part-time man still needs some work eventually to stay afloat, but the urgency and levels of financial commitment are obviously not so great (since if they were he could just revert to full-time), and employers will use rules of thumb rather than examining your specific financial situation.
Employers will never use part-timers (at the same or higher hourly rate as full-timers) unless they have to, which may be either because they cannot get full-timers or because their own needs are only for a part-timer - though they will of course readily hire part-timers who can be got significantly cheaper per hour than full-timers.
The latter is common with women I think, where a third-rate employer who can only afford to attract and retain men who are the dregs of their sector, may find a woman with children who has come down from much better (or who without children, would have gone much higher), and will get her part-time for the same hourly rate as men who would be dregs at that rate (and without violating any equal pay law, because the woman is paid the same pro-rata as any men in the same organisation, notwithstanding her higher competence and/or experience).
I would also imagine an employer might ask why a person is only looking for part-time work, aside from the possibility of lower outgoings. Is he decrepit and slow-paced? Is he sick or fragile? Are we playing second-fiddle to another part-time employer, whose demands may change and will come first? Are we a stopgap for a man seeking full-time work, now or soon? These things are unlikely to be asked outright, especially because any honest answer which would confirm these facts is never likely to be given by an astute candidate, but rather employers may surmise or speculate.
Bottom line, if the employer isn’t advertising for part-timers, and has no experience in working with reliable part-timers (or has the opposite experience), then those asking for it will be looked upon with deep suspicion as to why they don’t want or can’t do full-time.
A large number of quality candidates asking for part-time work despite being capable of full-time, in circumstances where the employer is also not struggling to get full-timers, would suggest an employer is paying far too high a rate - and he can afford to drop rates until the part-timers have to present themselves as full-timers to meet their living costs. If he cannot drop them anymore, for example, because of minimum wages or other strictures, then he will just refuse to hire you outright until your means have been degraded to the point you need full-time work (and are thus on an equal footing of desperation, as the man who was seeking full-time work from the outset).
While those looking for a 4 on 4 off shift pattern in whatever role obviously,rightly or wrongly,get painted with that same brush for the same reasons.IE the bosses don’t like to think that the job is being made too easy. 
Well, the tradition with 4-on-4-off was that you worked more hours per day than the standard 8, and often that it was combined with shift work. It wasn’t designed to make things easier for workers.
If particular bosses are resistant to it, it’s more likely to be because they do not require equal manpower at weekends as on weekdays, or because for whatever reason they can’t readily find enough workers in the market who will participate in it.
You’re nothing if not predictable old fruit. Good luck in your job search, something tells me you’ll need it
