I have on going project in middle east, during the construction phase we have few work not identify during the tender and client told it is the contractor cost.
It seems you have been advised "... it is the contractor cost." What other advice would you like to have?
Is your client asking you to perform work not included in the scope of the original price tender? If yes, you are due extra money for this work. If he doesn't want to pay you for extra work, you are well within your rights to reject the request.
If the "few work not identify during tender" are not indicated in the bid (pre-tender) plans or specifications, you are due a change order (add to your tender) for this work and should agree on same before starting the additional work.
If the "few work not identify during tender" are indicated in the bid plans and specifications, you will not get a change order and will be held to the tender (contract?) agreement.
Review the bid (pre-tender) documents (plans, specs, scope of work narrative, sketches, pre-tender meeting notes, ect.) used to calculate your tender offer thoroughly before you go to battle on this.
The owner/owners rep/project managers desk is not the place to start thumbing through the project documents as your arguing this out.
Have all your ducks in a row before you initiate a meeting on this.
Good Luck!
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