Contractor Up-front Costs

[Kyler J Sloan]

Should I be worried if a contractor asks for an excess of 50% up-front, on the day of a contract's execution?

The job is a staircase renovation at 6.5 K, with 4.5 K upon the execution of the contract, and 2 K after its completion.  

He has completed one job for me before, but did not request so much upfront. Then again, this is a relatively small job.