Yeah, flagging on the *Recs.SE sites is harder in general because some of the usual spam indicators don't hold up.The largest problem with red flags is that, due to their inherent penalty, they tend to have a much sharper drop-off in where people draw that threshold. It's worse on this and other sites, where there has to be a higher tolerance for fishy links. Wordpress.SE has the same problem.
Most of us who flag over time have learned over time to run with custom flags when it's not clear why it's spam (especially if they're spamming multiple SE sites and we need to link to a Charcoal report to connect the dots). I find a higher degree of success with custom flags, and most mods have expressed a preference for them. The trade-off is that they are slower and they don't always get the desired result. Conversely, Charcoal has a handy tool to look at reports and issue a red flag via the API right there.
If I were to ask for something, I'd love to see there be a comment section for red flags. Not optimistic that will happen anytime soon (there's more frustrating things I'd love to see fixed), but having discussions like this helps in the long run.
