I think if you know what your generally bringing in the house it's fine. I would suggest finding some healthy tree roots, or healthy area with fungi. Or simply a scoop of really, clean, healthy smelling earth. It's all about risk factors.
If your working on a budget, there's lot of good alternatives. You can also get certain organism off of things like rice wash, grain washes, wheat, sprouting alfalfa seeds, ect... Some seeds are going to naturally sprout along with some native fungi.
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I can often identify many organisms simply by smells alone, and sight. But I have decades of practice. college background on this subject. It was also a small part of my practice for many years, assessing character. Pseudomonas aeruginosa
smells like flowers. Streptococcus milleri smells like browned butter. I've got quite the iron stomach for all sorts of smells, things like putrefied flesh, ect. I've worked with lots of infectious pathogens, for decades.
now it's a hobby.
Simply add bacteria (grain wash, or scoop yogurt) into a gallon of water, add something like 1/2 cup of unfiltered honey (best thing) or molasses, and allow them to grow. As for AM fungi, I would say best bet is healthy conifer roots, including pine, firs, spruce, hemlock, oak, hickory, alder, and beech, roots.
I even add in the occasional brewers yeast into my soils, mixtures. ie. Saccharomyces cerevisiae. Organism by no means need to be expensive. There all around us, actually, just need to isolate. But again; I do think the FF Microbrew is an excellent product, has 4o organisms, and is very reasonable priced.