"I don't like to drive a new car," he says, "because in Nablus there are lots of poor people. I cannot drive a very good car when people can't find something to eat."
Unemployment, Israeli restrictions on movement in and out of the city and rival Palestinian armed gangs within the city have all taken a toll on people's lives here.
A reputation for clean hands and caring about the people is why Islamist politicians like Mr Yaish, in alliance with Hamas, won 74% of the municipal election vote in Nablus.
Another reason is the continuing strife within the ruling Fatah party of Palestinian leader Mahmoud Abbas, like the temporary takeover of the election offices around the West Bank.
"It's a benefit for Hamas to be in the municipality or in the parliament. They will have to act as a political party not only a resistance party.
Maybe Hamas, listed as a terrorist organisation by the US, the UK and other governments, will be brought into the political mainstream. But the hardline militant party is unlikely to talk to Israel.
Mothers with babes-in-arms and bent-backed old men leaning on their walking canes try to plead with the young Israeli soldiers to let them bypass the hours of waiting. But they're sent to the back of the line.
"Hawwara Checkpoint is a key checkpoint for terrorists trying to smuggle weapons, even mortar shells, either within the West Bank or to carry out terrorist attacks inside Israeli cities," he says.
In a few days, the ceasefire with Israel that Palestinian militant groups agreed to last March will come to an end. It was never fully effective.
Israeli planes bombed areas of the Gaza Strip on Tuesday night, responding, they said, to Palestinian rockets. And the endless cycle of conflict shows every sign of getting worse.
In the narrow, dusty streets of the Balata refugee camp in Nablus, every shop front and wall is plastered with posters commemorating Palestinian fighters who've been shot or captured in gun battles with Israeli soldiers - they are shown holding their weapons proudly.
Short of jobs and pride, except as fighters, there is no shortage of young Palestinians in Nablus willing to take up arms. And there is no political process which they believe gives them any reason to stop.
One of the militant groups, linked to the ruling Fatah but operating independently, is the al-Aqsa brigades. Nasr is one of the brigades' leaders in Nablus.
"We're fighting Israeli units every night. The last two weeks they have come every night, especially to the old city and to the camps," he says.
"The ceasefire won't be renewed. Because the Israelis still occupy everything. For example, last week they killed three of our friends here in Nablus.
Yet the political success of Hamas politicians and the determination of militants to fight on against Israel is not only a problem for Mahmoud Abbas.
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