The other answers provide good descriptions of what may be happening with this particular scam. However, I wanted to add an additional answer to specifically address an incorrect (and dangerous) assumption you've made. In your question, you asked,
Is it safe to trust once after receiving a payment? or Do you have any ideas on any problems that might arise ...
You won't be making much money with it.
High performance computing is today happening on NVIDIA graphics processing units (GPUs) programmed with NVIDIA CUDA, not on central processing units (CPUs). For scientific computing, double precision is a necessity, and consumer GPUs, even if NVIDIA, do not have enough double-precision units in them to have an ...
The website is running a series of WebAssembly process.
As a computer program, it can do anything.
Use the computer as a proxy to conduct some "profitable task"
Use the computer to generate traffics to conduct click fraud
Turn the computer into a malware botnet, conduct illegal DDoS against some victim
doing some other "...