Finally i saw people bragging about they have 600-700K gold do they seriously make that money while wearing end game gear with this repair system? Or just grind for days in peasant cloths or something?
It varies from person to person.
Some people are lying.
Some people have sold heirlooms.
Some people do grind with peasant gear/cheap gear often.
Some people are gods when it comes to luck, as well as enjoying banner stacking and selective fights (though that is the slow way to accumulate gold/level as you have to pick and choose a bit when and where to play for optimum results).
Some people (a lot of people really) either use a class that uses end-game stuff that is still cheap (like Archers), or are multi generation and from the time spent as being a peasant for several dozen gens (playing through level 1 to level 17-ish helps gold, now imagine this for several gens) and the time playing a class that does not use much gold, they have accumulated a lot of money.
In short: Yes it is possible to use your "best gear" and still make a lot of money, though some builds will never do this quickly.