The more I think about this it seems that in RPG publishing reciprocity marketing is easy to do. We can quite easily create free digital assets, with the intention of giving them away.
The other big advantage of giving something away for free is that those people may well join your DTRPG mailing list, or become an Itch follower. How useful this is, people who are signing up just for freebies, are not the best customers.
That is still a form of reciprocity, you give them something for free, they sign up to receive your emails.
Reciprocity can be more or less hard sell. This week, my email about Angus was very much soft sell. I had no intention to garner so many ratings, I just wanted to get some ratings to counterbalance Angus and the 3* banditry.
When I tell people that they can use the full-size preview, I am not intending to trick people into buying stuff. My goal was twofold. Firstly, a well-informed customer will buy a book if it is the right thing for them. Giving them the entire book to browse through is what they would get in a bookstore. Secondly, I don’t want poor ratings from people who expected more than my booklets provide. I am intentionally rules-lite, and that could be ‘not enough’ for some people. If they have seen what they are getting they are or should be less likely to give negative ratings or reviews.
In contrast, my email sign up was 100% intentional “I give you the Alien solo rules, you give me your email”. A fair exchange is no robbery. People are unlikely to, or less likely to, just give out their email address without some kind of relationship. Reciprocity creates that initial relationship.
I suggest you read a bit about this method, decide what you are comfortable with, and what is within your capabilities, and then apply it.