The 145/146 models are basically the same, however, there is a distinct difference between the pre-1997 model and the post-1997 model.
Up until 1997 the 145/146 had Alfa Romeo's flat-four engine, this came in two guises 1.6 single overhead camshaft and 1.7 16 valve. With both these cars, it is necessary to make sure the cam belts have been changed, and on the 16 valve, it is advisable to also change the idler and tensioners.
The only weak spot on higher mileage cars is the synchros on 2nd and 3rd gears, the latter car has a different gearbox so this does not apply.
On later cars with the 16 valve twin spark engine, it is important to have a comprehensive service history and a recent cam belt and tensioner change (Cam Belt Change Offer) is always an advantage, as if it has not been done within 36,000 miles (or 3 years, whichever is sooner) it will be the first job you need to do. These engines can also make a rattling noise on startup that sounds a bit like a diesel engine, this is most likely the cam variator and while it is not essential to change it, as the car will not breakdown, as a result, it is probably best to get it replaced with the cambelt. If the engine still rattles when warm it may be due to problems with the engine bearings and it would be advisable to get a mechanic to look at it. Alfa Romeo engines use oil it is advisable to check your new car regularly until you get a feel for how much she uses.
The suspension on Alfa's 145/146 is relatively simple with McPherson struts at the front and radius arms at the rear. The lower front wishbones (145/146 lower wishbone replacement guide) wear on the inner end at the front and this will often show up in worn inner edges of the front tyres. While the bearings on the radius arms will wear if the car has been used on country lanes where the ingress of dirt can cause premature wear. When on a road test make sure you take note of how the rear of the car feels, if it is soft and wallowy it may need rear shock absorbers.
Corrosion is not a major problem on these cars but they are getting older now so it is important to check the floor pan for corrosion. If there is any, it will be along the rear edge of the floor or next to the sill. the electrics in the car are generally quite good but be aware that if the airbag, ABS or injection lights stay on you could be in for a large bill, all these warning light's should illuminate for a few seconds and then go out. If they don't come on at all, suspect that someone has taken the bulb out for malicious reasons.
The interiors and bodywork on these cars are generally hard-wearing however there is a tendency for red cars to fade, and they don't always fade at the same rate so they can end up as various shades, this must not be mistaken for accident damage.
I hope this is of some help to you and remember if you have any doubts it is best to walk away or at least get a competent mechanic to look at the car for you.