From what I know, Its possible to have prop listings/fake listings of something like oxym30s and they be fent instead. Obvoiusly needs trust from both yourself and the vendor/seller, but that is the only way possible. I did that once, when buying a rifle for ireland.
"Bad" is subjective. Sure, there are plently of substances that are terrible for your health but the main issue with fentanyl is the dosing. It's extremely potent and very easy to overdose on. LE obivoulsy targets every market but if a market specifcally advertises sales of fent, I could absolutely see them prioritizing that market.
In practice the Dreads ban on fentanyl applies only to the raw or uncut product. You cannot source fentanyl under it's own name on Dread. This is not in the global rules, but is generally observed accross the platform. I wrote the first 2 paragraphs of the /d/Opiates fentanyl policy for /u/effwrk, who was a moderator on the sub at that time. I did this under my previous /u/plkqcs account. The policy prohibits sourcing fentanyl under it's own name. Users can only source this chemical under the name of it's consumer products such as China White, Synthetic Heroin and Oxy Presses where it is cut down to roughly one 100th of it's normal potency. This prevents the scouring and sale of raw fentanyl which has proven to be a danger to the community