The legal status of a courier isn't something that you're going to have to worry about very often. First of all, you have to finalize what you mean by it when you tell yourself that you're worried about a courier's "legal status". Does this mean that you're wondering if your San Antonio courier service maintains proper insurance on all their vehicles, or if you're curious as to what kinds of hiring practices they have to ensure that everyone who is driving for them is safe and bondable?
The first thing that you need to realize is that almost no company could stay in business long, especially not in a high risk field such as the courier industry, if they were employing any tactics which could be questionable legally. There are simply too many situations in the courier industry where a company could find themselves extremely liable for this type of action, so if you want a good general indicator to the legal status of a courier company all you have to do is check and see how long they have been in business. If they have been around for awhile then they are probably very much on the level.
Most courier
companies have very good employee screening programs in order to make sure that only safe and trustworthy drivers are carrying your goods. However, if you have reason to doubt this for any reason then you should ask the courier company what their practices are as far as establishing the security and trustworthiness of any given employee. You might also want to make sure that they bond all of their employees. If they can't get their employees bonded it might show that they are hiring high risk people that you may not want responsible for your goods.
In order to stay in business, a courier company is going to have to maintain the minimum amount of insurance required on their vehicles and cargo as determined by the law in their state. However, couriers are used to being asked to show proof of their insurance, and are usually happy to demonstrate this to their clients. If this information doesn't prove enough to you and you have adequate reason to suspect that a courier is operating in any kind of illegal manner, your only option is to contact local authorities with your suspicions or at the least to stop doing business with the courier.