A starting point would be to find out what they used to program the THS site ten years ago: TrustedHousesitters - Marketplace - Case Study | Sunscrapers
Or just call them (in Poland) and ask: https://sunscrapers.com/ (that b/w group photo down the page confirms some prejudices about computer nerds…)
I suspect this is not too difficult to achieve. When my IT geek was 16 I asked her to come into my work to help with a very boring task of taking data from a program we were getting rid of, converting it to a pdf document and then uploading to the new system.
I estimated 2 weeks of work and agreed to pay her on that basis with extra if it took longer. I did not agree a reduction if it took less time as it was a minimal summer job rate anyway (lesson learned)!
PM of Day 1 I went to check on her to see how she was getting on to find her playing on her phone and not touching the laptop!
I asked her if there was a problem and if so why didn’t she come find me. She said no problem the program she had written was working fine. The first program needed her to hit enter at the end of each record so she amended her program so all she had to do was set it off! 
I asked how long would it take to finish all of the work. 3 days max!! I said I agreed to pay you for 2 weeks of work. Her response… you paid me to complete a task that would take YOU 2 weeks to complete. I did it my way, same result!
She is now in the 3rd year of Uni studying computer science! The future is bright
I need to find a 12 year old to explain this to me 
This is how people in IT/programming are getting overemployed (2-4 jobs simultaneously) with remote jobs haha
Update: the sitter has now applied (and been decined) 4 times within 24 hours.
If they are running a Bot script then they need to reprogram it to remove sits that receive a rejection, I know someone who can help if they need it.
Have the messages you have sent with the declines been read? If they have then possibly not a bot and more likely to be malicious (or stupid 
).
Sounds like a bot to me: 4 repeat applications within 24 hours. E.g. the sitter is probably using a script that automatically puts in an application every time a listing appears with X pet in Y location.
So you reject them, and if that means you’re now under 5 applicants, your listing goes out of reviewing mode & reappears on THS. The bot picks it up, sends the message, you reject them, you drop under 5 applicants again, the listing reappears, and repeat.
On that note, I’d probably report this sitter to THS so they can look into it. E.g. if bots are being used here to beat the 5 application limit, that’s not a good thing…
I too had reported a sitter earlier this year that I had to decline 5 times over a few days before they stopped applying. I’m not sure if it was just ignorance about how to use the site even though they got a nice decline message each time (except for the last time was a little less polite) but could have been a bot 
thankfully it hasn’t happened again. And no it wasn’t a previous sitter.
I reported the sitter to the website and explained that I already explained why I declined the application. The response was more or less a brush-off.
From TH Representative:
"I am sorry to hear that the sitter is continuing to apply to your listing. Please do be open with the member and let them know that are not chosen for this sit. If they require additional assistance we are always here to help them.
I do hope that this information is helpful and that I was able to resolve your issue. If you have any more questions, please do get back in touch with me. I thank you for being a part of our pet-loving community."
That sounds as if AI Frankie generated that response…
Soon the whole internet will be taken over by bots.
I would specifically report that the user appears to be using a bot to have them automatically apply to listings as soon as they go live.
And that as such you’re reporting them, such that THS can further investigate whether some members are now resorting to bots to put in applications in order to beat the 5 application rule.
Nothing in the T&Cs that says you can’t use a bot … ( not that I do - I have no idea how I would use a bot )
Since THS uses a chat bot to answer members questions I don’t think they can prevent genuine sitters from using a bot to submit their applications .
An unintended consequence of the 5 applications limit perhaps ; but it was inevitable that some sitters would start to use technology to assist them with their applications .
I know some homeowners use AI to assist with making their listings more attractive as it’s been discussed in this forum.
The idea of being able to block a member from applying would be one wait to solve the problem of multiple applications from same person.