Unfortunately there has been a lot of scaremongering in recent times when it comes to blogging. Google said it would crack down on spammy guest posts, then some SEO "experts" declared the end of guest blogging, or prophesied the end of blogging in general.
It's all cobblers as long as you remember it's about quality and relevance. If you have a blog about ice cream, then having someone guest blog about Forex trading is clearly spam. Likewise if your blog is nothing more than a collection of guest blogs of varied subjects, then that looks more like an article directory of yesteryear.
But having occasional on topic and good quality guest posts on your blog are absolutely fine. Problem is finding them.
Assuming your blog is about bulldogs, then you need to become the go to resource about bulldogs. Invite other bulldog experts to do a post, maybe breeders talking about things to look out for in puppies. Maybe you could invite a vet or expert to write about typical health conditions of the breed. Can you contact any competition winners, past and present. Maybe they could write about the excitement of winning a trophy, or telling owners how to go about showing for themselves.
If its your blog, keep control of the content and direction. Once you have obtained credibility and and popularity, people will naturally approach you and ask if you can publish their posts.
No magic bullet, just hard work reaching out and forging contacts, but use social media to find your target audience and approach them. Worse they can say is no