It is impossible to know if your client is or would become a stalker. The fact that he sent a thank you E-mail after his first session with you and wanted to see you again the next day, does NOT make him a stalker. He may have really enjoyed his time with you and can not wait to see you again.

Of course, we were not privy to what he said during the session or what he wrote in his follow up E-mail. If he said things that were inappropriate (i.e. perhaps continually hinting at a long term personal relationship with you) or he acted inappropriately in any way (i.e. doing something over and over after you asked him to stop), you have EVERY right not to see him again. Whom a lady chooses to see is her call and no one elses. If you are "creeped out" by this particular client, then do not see him again. Period. There is no point is going through the mental anguish of worrying before, during or after the session, if this hobbyist will cause you any harm. And further, you do not owe him explanation of why you are not seeing him....and besides, certainly nothing would be gained by telling him the real reasons.

I am sure at times it is very difficult for a provider to distinguish between an appreciative hobbyist who simply enjoyed their time together and wants nothing more (other than repeat paid sessions) and a hobbyist who is showing signs of crossing the boundary and is bordering on inappropriate behavior (i.e. incessant messages, phone calls, wanting off the clock time, etc.)I suppose you just have to go with your gut (whether right or wrong). If this hobbyist makes you uncomfortable, than do not see him.

I often get follow up emails from clients, to thanks me and tell me how much they enjoyed our session. Some have told me they can't get me out of their head. Most have become regular clients.
Not every guy who says this turns into a stalker. You will have to use your own judgement, trust your instincts.

Speaking from a client's perspective, I would say it's not uncommon to have a strong emotional attachment to a provider. I've found myself missing the girl an awful lot, as if we had something more than a professional relationship. Of course, I try not to let those feelings get the better of me, and I've certainly never let them turn me into some kind of stalker.

So, it's possible that this guy is just feeling the kind of puppy love that a lot of clients come away with after a session. After all, it's only human nature to associate intimate feelings with intimate acts.

That said, your safety is paramount. If you're getting bad vibes from this guy, do not see him again.

It is your business and you need to do what you feel comfortable with.  If the guy sent creepy vibes, then by all means, do not see him again.

If you are attractive & talented, then are plenty of guys who will be trying to get on your dance card.

Great sex tends to stir up the emotional attachment hormones...   In the evolution of the human species, this is good...  for NSA sex no so much.  Newbies need to learn to control this.  I find it is more likely with inexperienced clients.  The cure?  To see other ladies.
HE should realize he is crossing the line.  I have realized it im myself, early on...  and I swiftly corrected myself & see more than one  favorite lady.
I would not let some client rebook next day...  shows he's not in control.  It may have been great.  You may have enjoyed him too.  You may even like him.  But this is not going anywhere.  This is not a civie date & he needs to know this.  
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It's your life, your safety and your piece of mind. Always do what feels right.  Unfortunately the only way to find out if a guy is a stalker is after he starts stalking you.  If you feel uncomfortable with a customer it's best to just stop seeing him.

I for one always follow up with an email of appreciation after a visit and on two occasions have requested a visit the very next day simply due to the great time I had.  I don't think that those two things make one a stalker.  As the others have said, trust your instincts and err to the side of caution if you must.

Is this a well know hobbyist, with multiple reviews and some local board posting presence? If he known, and has history, he is probably OK, means he has or is seeing others and you just really rocked his world.

On the other hand, if he is unknown, be careful.

I am a strong believer in trusting your instincts, intuition (for you ladies), or the little hairs on the back of your neck, if it feels like something is WRONG, there probably is.

Be safe first, ALWAYS!