Quite a lot, even between tests that share the same technology name. Four key things that vary between providers include:
How well the collection kit stabilises and preserves microbial DNA on its way to the laboratory.
Laboratory accreditation.
The bioinformatic pipeline used that turns sequence data into named organisms.
How precisely species can be identified and their relative abundance estimated. Two tests can carry the same label and still produce meaningfully different profiles from the same sample. It is reasonable to ask any provider how their method handles each of those four steps.