I have purchased a fairly new Toyota Avalon and have decided to buy
the Platinum Extended Warranty. I have note that many dealers sell
this policy. One in Massachusetts, http://www.toyotapartsworld.com,
has a good price.
So here is the question: How can I find out if this is a bonafide
company and not a scam?

Thank you!

From experience and research - the best warranty is one from the
manufacturer.  The risks are too great if you buy one from an
insurance company that markets car warranties.  The two major risks
are: 1) the health of the insurance company. Many go out of business
and leave you with no coverage even though you paid for it.
 2) they have clauses in the contracts that almost make it impossible
to collect if you make a claim, short of suing them.

Better to put the money aside for repairs or better yet, use it for
preventive maintenance.  At least you will get some benefit from the
money.

If you do get a warranty do all the preventive maintenance called for
and keep every single receipt.

In my case, I paid over $1,000 for a third party warranty and they went bankrupt
after a year into the contract.  Don't fall for the hype about how solvent they are.