In general, choosing a reputable money order company is typically about finding a company that will fulfill your needs, has a good reputation, and is well established. If you have time to do some research, then you should look at the website for any company you are considering to be sure it provides the services you need. This includes issuing money orders in an amount that works for you, providing sufficient places for a money order to be cashed, and providing means for tracking money orders. If you live in the US, then you may also want to consider avoiding a private money order company and using the US Postal Service.
A money order company is a business that issues, and potentially cashes, money orders for use by individuals and businesses. Money orders are similar to checks in many ways, except they are paid for in cash and backed by the issuer of the money order, rather than by a bank. A money order can be issued by a private company or by a public institution, such as the Postal Service in the US. The different services offered by such a company will often give you a good idea of how reputable that company is.
For example, a money order company should have a large number of locations where the money order could be purchased or cashed. These are not always the same locations, and even reputable companies may have locations that issue money orders but do not cash them. Doing some research is one of the best ways to ensure that a company is reputable. You should look for complaints against them through consumer rights advocates or similar organizations, and be aware of any issues or stipulations the company has regarding how refunds can be requested and money orders can be tracked.
If you are unsure of the reliability of a money order company, and you live in the US, you can always use the US Postal Service. Money orders can be purchased and cashed at just about any post office. International money orders can also be purchased at post offices, and these money orders can then be cashed at the post offices of participating countries such as Japan and Canada. As a government agency, the Postal Service also tends have more oversight and regulation than a private money order company.