On a private mailing list there was some discussion, and I had an outburst. Summarising very roughly, someone said bad things about their competitor, without (at first) offering any justification. Here's a version of my outburst, edited to remove references to the actual topic and identifyable people. I thought it might amuse me in fifty years or so to see how full of myself I was.
I have no experience with this service. Or the person saying bad things about them. I am entirely ignorant about everything. I am not biased towards or against any of them. There's another point I would like to raise. Or rather, an opinion I would like to express. I feel very strongly about this.
There are two reasons to not show respect. The proper reason is because the target has thoroughly proven themselves to not deserve it, by their words and action, or lack of them. The wrong reason is anything related to anyone else than the target: your own low self-esteem, your fears, your evil schemes, your own bad day.
Even when the right reason exists, it is a sign of respect to the audience to be respectful towards someone who does not need it: it avoids shoving the discussion down the drain. Showing respect, even when undeserved, indicates strength and moral high ground. (Please note the difference between showing respect to and agreeing with or approving of the other party.)
To me, as a total outsider, these remarks about the service give a bad impression, but not of the service. It may well be that they are a scammy corporation that gives lousy service. However, nothing in this discussion has given me a reason to think so.
They may be well-known in your circle. They may be well-known for their bad quality and bad service. But the rest of us don't know that. When you denigrate them, you just look like a whiner. Especially someone who wants to promote their own service over that of a competitor, looks bad, because they're saying bad things about them, without giving any reasons.
If you're going to be criticising your competition, you need to be very careful of how you do it, or you'll look bad instead. Or also, since it's easy to make everyone in a discussion look bad.
If you'd like promote your company you can explain its virtues and benefits and the good deals it provides. You don't need to denigrate anyone else.
If you'd like to get people to avoid your competitor, because they are bad or evil, then show why they are bad, or evil, with examples and references.
 This is a true statement in every context.
 After decades of experience as a whiner, I have a finely tuned sensor for detecting fellow whiners.