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Just bought a new set of tyres for my 2004 Mazda Demio (Imported used)
The tyre supplier recommends pressures 2psi higher than car manufacturer - who is right?

Reading other tyre questions on this forum, I see you refer to checking pressures regularly.
At what intervals?

The reality is they're both right. If you're checking pressures when the tyres are hot, the pressure will vary slightly from starting off cold, so it's not a totally exact science anyway. While it's important not to grossly over inflate tyres as they will wear in the centre of the tread, it's more important not to under inflate, as low pressures will wear the edges and damage the side walls, as well as increase your fuel consumption and compromise the vehicles handling.
Tyres will lose pressure over time, so your tyre supplier's suggestion of running a couple of pounds higher than manufacturer's recommendation is taking this into account. As you can see, it's better to be slightly high than low.
Try to check your pressures once a month.

BarryB should consider himself lucky to have had only 2psi over the prescribed pressure. I have had from a well known retailer my tyres at40psi. on a toyota camry. Every time i have had tyre work they are always hopelessly overinflated.The wheel nuts are always overtightened,on one ocassion the studs were ruined at a company that does a lot of tv advertising.I would not trust any tyre company.

tjhull raises another good point here. Wheel nuts should be tightened with a torque wrench to avoid over-tightening. Good tyre outlets adopt this practise these days, and the days of tightening the nuts with a rattle gun until they can go no tighter should be a thing of the past.