Ask a bricklayer to build a wall but demand that its made of lego bricks and it will take longer and so cost more.
Ask a bricklayer to build a wall but demand that its made of cannonballs instead of bricks and they might give it a go but will build in some contingency for unknowns and so it will cost more and the wall will probably not be much good.
Ask a bricklayer to build a wall but to use butter instead of mortar and they'll build the wall on the understanding that they aren't held responsible when it falls down.
Ask a bricklayer to build a wall using sugar lumps and they'll probably turn down the work.
Ask a bricklayer to build a wall and you'll be fine.
A Tradesman was asked to provide a quotation for painting a wall.
The customer accepted the quote and specified that the colour of the wall should be "Tartan".
When the Tradesman pointed out that that wasn't the basis on the which the quote had been estimated, the Customer responded "What's the problem - just get a can of Tartan Paint".