For me if they start asking for discounts or texting too much (asking for nudes or making too many questions), there are red flags of a bad client.
Be strict and never treat the whole interaction as if it was a hookup. Don't be too nice. Be respectful but keep it professional, direct and short. I once had this kid that had the nerves to ask me for a discount when he saw I was too nice. He had the audicity to tell he could only pay me half the price once we were done. I was so disgusted. My guts were telling me something right before we finished. He was a really bad client.