Treat them as they treat you. If you're going to meet a WG with the mind-set that she deserves no respect and is doing a degrading job, then why exactly are you there? If when you meet her, she's all smiles, cheerful and is clean then you're most probably going to have a wonderful time. If she can't be bothered to smile or clean herself or her place up, then bugger you respecting her, she evidently doesn't respect herself.
Sadly, from my experience the vast majority of WGs do lie and cheat, however by just brushing this off you merely enable them. If she states it's £60 for half an hour and then asks for £80, just walk away. Always check everything before handing any money over, if you find something off, just walk away. Sure she'll probably refuse to see you again or write horrible things about you on the web, but at the end of the day it's her loss.