It's usually fairly simple,... if you suspect seeing a 'street-walker' struting her stuff on a corner, just pull over nearby, beep the horn if you don't have her attention. KEEP YOUR DOORS LOCKED and WINDOWS UP, except for ONE of the windows, depending on what side of the street you parked relative to where she is... crack that window open a little bit, enough to hear the conversation, and if you like what she's offering, then let her in... if she's weirding you out, like talking stoned, crazy or "cop-ish",...don't think, just drive away....
If you're asking about how to avoid 'entrapment', unfortunately there is no surefire way to defend against that.... *obviously don't take legal advice from this website, lol... but asking if she's a cop doesn't fly anymore with judges (from what I've heard), but instead you could ask for a "freebie" in the form of a nut-squeeze, or ask to see her tits, maybe ask to sample-squeeze yourself, or perhaps ask if you're allowed to take pictures.... how she reacts tend to show redflags, if any.. or really good acting on the cop's part... I can't see how a judge would accept a UC grabbing nutsacks as a form of entrapment or not....
If you're confident enough to know that she's the real deal, and you let her into the car, go to a place YOU are familiar with, not her suggestion... don't let her tell you where to go. So before you start prowling, scout out any quiet discreet venuez in a 10 block radius that you would take her... Having her lead could set you up for getting arrested, scammed or mugged with her pimp waiting in her special place.
Prowling on foot just ads more risk to the game. Makes it more thrilling, but more dangerous since you're not protected inside your car. Walk casually, stay calm and cool. Look at everyone you walk by, make eye-contact, read their expressions, let them do the talking first. They'll usually open with, "hey, got a light?" or "do you have a cigarette?"... something to break the ice with, followed by small talk about the weather or how quiet the evening is... however the conversation goes, you have to let her make the offer, not you... She might look like a 'walker', but these days girls all dress the same anyways... she's probably on that corner so her friend can pick her up going to the club?... it's best for her to lead the conversation and see where it goes.... best case scenario, she'll take you down the alleyway behind the dumpster. At mild, you're out a single cigarette. At worse, she'll scream 'assault', and kick you in the nuts for being a pervert and hope there is no cops around.
The rest is common sense stuff... Hold on to enough cash to make a reasonable deal, don't carry more than you think you have to; that way if you get robbed you're only losing that what you were planning to spend in the first place. Don't bring your wallet (hide your Driver License and CC in your sock or shoe or under the seat), No rings or necklaces on your persons, or loose cash in the center console, even insurance papers or anything in the glove compartment with valuable information.