Research, research and research. I have many clients who think due diligence on a placement agent can be done via email or a phone call with no money spent. There are certainly first-level reviews that can be done, but to do serious due diligence, court records, background checks, prior clients, etc., all have to be researched. $150 million is too much to invest without spending money on due diligence. I have been involved in due diligence around the world and it's surprising how many scams and less-than-reputable placement agents are promoting themselves.
It is all subject to the sector and, most importantly, the requirements you need from the placement agent. Make sure you conduct a due diligence and the capability for them to raise the necessary capital. I always prefer smaller firms, as they will give you a tailor-made solution to your requirements, rather than the bigger investment banks.
If you don't know any, your U.S. professionals can usually make some good recommendations for placement agents. That size deal sounds on the small side, after appropriate debt levels, so it would require a second or third tier firm, I would think.