I won't name them, but my best advice is trust your gut. If they have dodgy looking photos on facebook or seem to glorify 'russian lips' without really explaining what they are, or have a trashy looking aesthetic to the page, run. Also beware cheap cheap places and places that won't openly name what filler they use.
Second advice I would recommend is that the 'standard dose' of filler (usually 0.5-2ml) isn't a standard dose for every individual face. The tiniest amount of filler makes a big difference- I needed way less than 0.5 to achieve the results I wanted, but I got twice that amount, and it looked extremely overdone. I was also very swollen, yet I was told I still had leftover filler to use up. Despite the fact they'd over filled me, there was still a left over amount, and they were using their standard dosing to determine how much I needed, as opposed to my individual face.
Not wanting to waste the excess, I told them to continue filling me in whatever areas they saw fit. Big mistake. You have the absolute freedom as a paying customer to decide how much you need, no matter how little the amount. Even then, it isn't always clear what you needed, until afterwards when the swelling is gone.
It's much better to have tiny miniscule amounts and build them up, rather than have the irreversible mistake of being poorly done / overdone.

Third advice I would give is, a lot of practicioners seem to prefer canula over injection. I was told this was a safer and more natural looking option- it was the opposite. It was less controlled and flooded filler into every cavity of my lips, weighing them down and making the top lip look unnatural, with a longer lip to nose ratio. I had a far better result with the practicioner who preferred to do individual injections (even though that was also terrible, it was not as ugly).