Well I will tell you this much.. its an organic nute solution and it does settle and separate over time.. however I've always kept it in the original bottles so I've never seen the real degree of separation that takes place. Now, that being said, I personally would never trust buying something like that from an individual online breaking down something like that and selling in smaller quantities. The profit margin probably just wouldn't be that great, without diluting the solution down a least a little bit. You would have to research his reputation and determine if hes some sort of normal business or just a random guy looking to make a little bit of cash. There are ways to test solutions for the amounts of individual/specific nutrients. By doing so you could look at the original mixture of big bloom and compare with your test results to see if there has been significant dilution or not. Some methods of doing this may be much more accurate than others, I haven't done much of this so I can't tell you much more on that but its worth a shot if you can do it cheap. Just don't spend so much that it would make more sense to just go out and buy an original full bottle of big bloom.

As far as how to apply the feeding schedule, its pretty simple. Just use a larger container to mix the solution up based on the little packet you probably have or found online. Then apply it to your plants as they need it based on how often they require watering. If you're trying to mix it up smaller, single use mixtures each time you plan to feed/water you're going to have to put more thought into calculating the mix ratio based on the amount you're planning to use. Its best/easiest to mix a larger container once, and just pour out what you need from there.

Hopefully that answers your questions, if not feel free to elaborate on your specific concerns and I'll check back to address those in a timely fashion.