I enquire about Filming/Photos whenever I think an opportunity is there, which is (obviously) when it's listed as a service, or (less obviously) if I get a feel it might be offered by judging the profile. Unfortunately I don't have a high success rate

I reckon it was easier to get filming agreed years ago, before the rise of the Instagram model trend. I did film/photo a few SPs in the 2000s and 2010s. I have had some luck in the past few years, most recently Cherry (AW ID 6301887), who was fit but not an A* punt overall, yet the movie was nice. I do like watching the material back, as a reminder that as I get older I have had fun with some lovely beautiful ladies.
It used to be a lot cheaper to film but some are still affordable, like Cherry @ £240/hour incl. filming - though she wears a mask. I fancy doing Ivana Hyde, she looks fit and doesn't wear a mask, but isn't cheap either @£450 for the hour incl. filming. One of the best I did was Ivy Ray, again not cheap but she played up to the camera and it was like a proper porn shoot. Lily (7113521, no longer working) was one of the best @ £230 for an hour including filming... she was a lot of fun and a genuine nice girl.
I find it's best just to use the phone and even better if you have a spare phone, so you just place them at different angles and get on with the action. Some POV is nice but this interrupts the action. I find it's best going into a 'filming' punt with the understanding that the action will be centred around the camera and that it won't be a regular punt.
Always on the look out for more filming opportunities and happy to share/help out if anyone has questions.