Hey mate,
Quite a few members here sell on. I do it really just for fun but a bit of beer money.
Best tip I can give is get yourself a good carby cleaning kit and air compressor and get used to changing pull cords and cleaning carbys. They are the main problems I come across.
I actually just revived a victa with briggs classic 4 stroke (I'll be selling for $120) that I was given as payment for servicing a Sanli for a bloke down the road, Well I say revived but really all I did was empty the foul smelling off petrol from the tank and replaced it with fresh petrol.
Whipper snippers are generally not worth the trouble if you are looking for profit - too time consuming and not worth much anyway.
If you are looking to start doing it seek out a parts mob to get cheap parts from. The bloke I found gets great prices and passes on great savings.
AND if you're going to start doing this make sure you do the repairs properly - dodgy jobs are dangerous jobs AND it gives the rest of us a bad name. (Not saying you would do a bad job). There are a few dodgy brothers in Adelaide who just make up bitsa's and sell them on for max profit without properly testing them or making them safe.
There are some bargains and great profits to be had if you look hard enough. When I come across cheap/free machines anything newer than 1990's gets fixed and resold. Anything older I fix up and keep for myself - not worth enough to sell and well I just like them...
Pete