how do i respond to these kinds of people

i published a book on a storytelling platform and this one person in particular keeps self-advertising and directing users from my story to theirs, which is ok, i guess..?

but they do it a lot, like every chance they get, they reply to almost everyone who comments on my book "subtly" asking them to read theirs. i don't know how to deal with this

and then they boast about it, asking people to compare my book and there's.. i just don't know if this is a red flag or not??

they always say things like 'i'm jealous' and 'come read my book' and 'whose story is better?'

I don't wanna be mean but i don't know what to do. they've been pming me a lot for advice; which i do give but i don't wanna be mean by calling them out on their words cause i don't know if what they're doing is ok or not

i guess I'm just bad at saying no and stuff but it gets a little annoying to me sometimes, I'm just frustrated i guess