I'm attending a non denominational bible church who are having a flea market. There are having a yard sale at the church's property. What's your personal opinion on this?
I don't see a problem with it. My church does things like this all the time. It's a good way to raise money for church expenses or different programs, ministries, families within the church who might be down on their luck,etc.
Is this a role of a church?
No but it is a good way to raise funds to help the church carry out it's role.
As Walter Martin once said, "The Gospel is free but somebody still has to pay the light bill".
Didn't Jesus said don't make my father's house a house of merchandise?
No.
What happened in that case isn't the same as a church holding a yard sake, bake sale, etc to raise money for the operations of the church.
In that case, the merchants were taking advantage of the faithful Jews who came to Jerusalem for the census but who still wanted to be faithful to God's commands.
The pilgrims came to the temple to make their sacrifice and the merchants took advantage of their piety and their desire to be faithful to God by charging them outrageous amounts for sacrificial doves and sheep and pocketing the money for themselves.