Firstly, you must realise that the is no such thing as safe sex. Just “safer sex”. There is always an element of risk involved and you must decide the amount of risk you are willing to take. Using a condom is a good step and if used correctly will protect you from HIV, gonorrhea and chlamydia. But may not be effective against HPV (genital warts), herpes or pubic lice. Oral sex without a condom carries a small risk of STI’s but the risk is there.
Some red flags for an unsafe punt:
1. She is willing to offer sex without condom at an extra price.
2. Signs of drug use.
3. Personal hygiene. Does she shower between clients. Are there clean towels etc.
4. Check her reviews.
I hope this is helpful.