This is a big problem. Some of my clients stick with me
because they know they can always call and get a quick answer on an issue that is too small to justify the whole formal engagement process and associated administrative burden. Whenever I see that it becomes a pattern, or I feel that I'm being taken advantage of, I try to move towards a retainer-type arrangement. Just saying NO (even in the most gentle way) has already cost me a client or two.
In these difficult economic times everybody are looking for freebies. Not because they don't appreciate we deserve a return, but because their budgets are so tight. In medical devices in general, and in regulatory affairs in particular, the turnaround is so long, that many don't appreciate the huge difference a sound advice in the early stages can make later on. The bigger companies usually have their in-house experts or they work with the big service providers and wouldn't bother hiring an independent specialist; so, we are often left with start-up companies employing inexperienced engineers and/or "Dr. Entrepreneur & associates" who are great clinicians but sometimes know quite little about D&D and/or regulatory clearance; that makes it even harder to convince that the service is worth the $ spent. Just go a bit over the edge and they say "hey, that's not so complicated. I can do it by myself." (which might even be true sometimes). I remember that it used to be different before the GFC.

Ronen.