plenty of buyers guides around, john whalley has one on his site,club lancia sports,evocorner.
a few quick answers without going into too much detail.
1/ issues to look for:
bodywork - without going to extreme- rust at base of windscreen,rear roof, behind rear bolsters where turrets are to name a few.engine-turbo smoking, cambelt changes, clutch,suspension-drop links, etc
2/ evo1 vs evo2 quite a few differences between seats,wheels,engine management,turbo and odd bits of exterior trim. as for the car itself biggest pro is the resale value 2's seem to be holding out a lot more in value.
3/ answer no, all about getting a good sound reliable car thats been looked after,and has reciepts/proven service history be it a evo1 or evo2.
4/yes.
5/ buying a "top notch car" will be most likely known to the clubs,go to a few shows first and speak with owners if not then spend time looking, and get a full inspection first before buying,the highest priced car for sale does not always guarantee it's the best you can get.
hope thats of some help, i'm sure there are others who can write up a more complex buyers guide.
think the same potential buyer has now posted up on evocorner.i'm sure he will get all his questions answered there.(plus a few extras
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