While it's not impossible, Willoughby is not likely to have been shooting on Sir John’s manor. I feel this way because:

1. I agree that if Sir John found out that Willoughby had been shooting on his land, he wouldn’t be jumping up and down having a fit, but he is territorial about his hunting grounds; and he definitely considers it fortunate to be renting to a family of only ladies so he doesn't have to share: “and in settling a family of females only in his cottage, he had all the satisfaction of a sportsman; for a sportsman, though he esteems only those of his sex who are sportsmen likewise, is not often desirous of encouraging their taste by admitting them to a residence within his own manor.” (7)

2. While it would not be against the law for Willoughby to shoot on Sir John’s land since I’m sure he has a hunting certificate, it would be impolite imo, and further, Willoughby has not yet informed Sir John of his presence in the neighborhood. As a result, he might well be thought to be a poacher and find himself at the end of a gamekeeper’s barrel since, on hearing shots, the gamekeeper or Sir John wouldn’t know of Willoughby’s possible presence. No, they would not shoot him on purpose, obviously, but accidents in such situations were possible.

3. There should be enough game to suit Willoughby’s needs for a day or two at Allenham and if not, it wouldn’t hurt him to wait until he connected with Sir John or had at least sent him a message. My guess is that Willoughby was walking near Barton Cottage to hopefully get a look at any or all the daughters residing there. He would, of course not be able to talk to any of them, but it might satisfy his curiosity to know what the possibilities were if he could catch a glance. As luck would have it, an immediate opportunity ‘fell’ into his lap.

No one is saying (at least I’m not and doubt Robbin is either) that Willoughby goes around looking exclusively for unguarded gentry women. His main diet would be servant girls, tradesmen’s daughters and ladies of the night. On the other hand, he would quickly hone in on any unguarded women of class whom he might prey upon imo. I think he would find them more interesting, fun, and challenging endeavors than the general population of women I listed. A lot of young women were in and out of London, Bath, Brighton, resorts, etc. from other places for visits. Willoughby had the ability to talk women of Eliza’s and Marianne’s ilk for a ‘quick ride‘ in his carriage and such who would see themselves as doing nothing wrong and unfortunately might find themselves having been seduced. They would be dropped off where they are staying, and, unless a pregnancy resulted, go back to their permanent residences no one the wiser. They wouldn't have had to all have been cases where the female is lured completely away from their protection and with it being broadcasted amongst others. By the same token, it wouldn't have had to be a lot of gentry women either but just enough to manage to keep it under wraps and avoid the reputation as someone who meddled with gentry daughters now and again.

In my opinion the scene of Willoughby meeting Marianne is set up like a metaphor. The fact that he comes by with two pointers and a gun underscores the idea of ‘hunting‘ and the game is not just fowl, though foul it may be as he sets out to ‘trap/capture‘ Marianne by engaging her affections with no intent of returning them. Perhaps the word stalking as we think of it in today’s terms seems extreme but there is definitely something of this in Willoughby’s nature that comes across in his dealings with young single women without a strong male guardian which brings out the hunter/sportsman in him I think. And the text further implies that Willoughby keeps track of all that befalls Marianne and though Willoughby doesn’t let anything get in the way of enjoying his life to the extent that he can within the life he has made for himself, it speaks to fact that he lives with some regret apparently everafter...