What will you do, as a PM if a vendor offers you commission for buying his low quality product for the project other than the high quality?

Against PMP ethics ,............ although measue against planned quality

This is not a commission, this is kickback. 

It’s all about wrong practice and ethics in professionalism, in this situation just need report to line manager via an email (to avoid any confusion need to be document this complain). Any disciplinary action is out of PM job inhere higher management or project owner will decide what to do for this vendor.

to control budget doesn't - all the time - means low quality , as PM will not accept commission from any vendor for such offer ,

I DON'T USED TO PLAY WITH FIRE !

Negotiating the right deal with your suppliers doesn't necessarily mean getting what you want at the cheapest possible price.

You may want to negotiate other factors such as delivery times, payment terms or the quality of the goods.

Most business owners would view a good deal as one that meets all their requirements. But there are many other factors to consider, such as whether you want to do business with a particular supplier again.

Both sides should conclude a negotiation feeling comfortable and happy with the agreement. Negotiations can be unsuccessful if either side feels forced into a corner.

This guide sets out how to negotiate a deal, including setting your objectives, understanding your supplier's position and using the right tactics.

• Setting objectives when negotiating with suppliers
• Understand your supplier
• Developing a negotiating strategy
• Negotiating team
• Conduct negotiations
• Negotiating on price
• Running checks on your supplier
• Drawing up a contract for your purchase