I would be picky about it.
I used to be more lenient until a guy sent hacked 100 hacked casino links to a site of mine and essentially ruined something I worked very hard on.
Nowadays I always ask to see their website in advance (and reject them ahead of time if their website has any sketchy links, etc), where they want to link to (if they do at all, because in one of my niches I get an occasional guest poster that doesn't want anything in return at all), and send them a list of guest posting guidelines/requirements.
What I have found is that the authentic guest posters (the ones that you actually want to guest post on your website) are usually going to send you their website and often their name in the first email anyways, because they are proud of it. They usually let you know who they are and why they want to guest post on your website.
I usually skip the emails that are obviously templates sent out to 1,000,000 email addresses.
Those are spammers, and since they are spammers, in my opinion, they run a higher risk of spamming your site.