Why do members think its ok to rip you off

In the last year of trading on ebay i have had a pleasent time and dealt with lots of great members who have either bought from me or i have sold to them, but, it seems in the last 6 weeks that i have had nothing but trouble and have been ripped off on many occasions, how do they sleep at night ? i am carful not to fall in the trap of the scammers but these members are not the every day scammer who is out to take your money, i have just had to take two cases to paypal through members just not sending my items to me, a total of 35 spent and paypal awarded in my favour and all i got was 5 back, why bother i ask myself, am i really covered like ebay and paypal say? No is the answer..... this is not to mention the members who have bought working phones off me and swapped them with there broken models and claim thats the one i sent, yes you read that right, incrediable as it may seem but it happens, i now have to write the emi numbers down of phones i sell so i can check this should it happen again, also i suggest to any dealers like me out there to link themselves with a crediable site that check online fraud, i have just linked with immobilise.com and now check every handset i buy with them, and god help you if you sold me a stolen phone as i will report it to the special police squad set up to tackle this. In short this problem only seems to be getting worse and i for one would like to see any member removed and reported to the police for committing this crime,