Need some tips

So I might be purchasing a car tomorrow that has sat and hasent run in 3 to 5 years. The owners say they have tried turning it over lately but it wont fire (possible fuel problem?). Im just wondering if you have any tips as to what I should do IF i buy this car as in tune up. Should I change the engine oil BEFORE or AFTER running the engine (if i fix the problem ). What do you guys think?

Im just afraid of spinnin a bearing in start up because its sat so long, and or damaging anything else.

Im also thinking of tearing out the gas tank right away to clean out any shit in there and testing the fuel pump. As well as a fuel filter change

umm... change the oil before? if you dont get it started, well you lose some oil and a filter.

There's probably dead gas in there. Dump in 5 bucks see if it starts up.