My personal checklist that keeps me from buying impulsively (and I ALWAYS do this step by step pero in any order):
1. ) Check If the item I want will last for atleast 3 years. Syempre kung mamahaling yan dapat lang na I would thoroughly get much out of it. So far lahat naman ng binibili kong mamahalin never failed on me even once.
2.) I throughly research about the item and the seller that I'm buying from. Kung swak ba sa kin ang features nung item(this also applies to wearables and consumables) at kung maayos ba kausap yung pagbibilhan ko. Minsan kasi hindi yung item ang problema kundi yung seller mismo - mura nga yung gusto mong bilhin pero ang labo naman kausap nung nagbebenta, pano ka gaganahang bumili nun?
3.) Look for alternatives. Not of the item but location and seller - hindi porke sa mall nabibili at kilalang seller ang nagbebenta eh considered nang legit yung item. It's difficult to tell a fake from a legit one just by looks alone, you need to hold it, smell it and feel its quality - common example sa ganito is pabango at damit.
4.) Factor in other costs for buying it - magkano pamasahe ng balikan dun sa location ng pagbibilhan ko, need pa ba ng reservation/shipping fee, etc. Kahit mura ang item na gusto ko pero alanganin sa location at oras then di bale na lang. Makakabili ka nga ng orig tapos murang iphone 7 plus pero ang seller eh nasa kalagitnaan ng alanganing lugar ng maynila then syempre mag iisip ka muna.
5.) And finally, I calculate on how much money I will have left once nabili ko na yun. Pag mas marami ang matitira sa ipon ko after the purchase then i can rest easy at night knowing na hindi mabigat sa loob ko yung perang nilabas ko para mabili yung gusto ko.
TL:DR version, nagmumuni-muni muna ako bago bumili.
ALL of my sure buyers sumasadya pa talaga kahit malalayo ang inuuwian nila para lang makapag-meetup. 
