The key here is to not go too far but just far enough in inflating Vancouver’s already notorious and known social concerns. Believability is the key in deflating a Yuppy’s* hopes of having found the perfect neighbourhood and home, which you occupy and don’t want to give up. Basically you want to make it seem just undesirable enough so prospective buyers who show up with dreams of white picket fences and with their little girl in tow, will simlply, just, move along. These are all tried, tested and true.
It is entirely believable that prostitues have used your alley, yard or driveway as a place to conduct their business. You may have even caught them. If not, that’s ok. You can find condoms in school yards, in cemetaries and at bus stops, so placing a few used rubbers outside your place is perfect.
There is nothing more gross to a happy little family than having to deal with plague carrying rodents. Conveniently the city is full of them. It doesn’t matter if you don’t actually have them. Just leave a few rat traps inside the house. But make sure not to leave them too much out in the open. You want to make it look like you are trying to keep it a bit of a secret. Like you’re secretly acknowledging: “Yeah and there’s rats.” You can get bigger traps for outside. Put those at the corners of the house. Very scary. If you do have rats, and have the option, and a cat, leaving a gutted carcass by the front steps is a real homerun.
Just like the condoms but you have to be a little more discreet. If you live near a park these should be easy to find and will probably have disgusting dregs of blood in them, which is a definite Yuppy* deterent. But of course if you are going to go needle pick BE CAREFUL. Use thick gloves, or even tongs and a bucket. Even better, get your roomate to do it. Otherwise get new, clean needles, draw your own blood and decorate away. For authenticity, shady corners, back corners and bushes are the best. A little splatter on the fence is probably too much, but this depends on how nice your house is, and how far you are prepared to go to keep it.
This one is the hail mary and only works if you do actually live near a sewer system, or pipeline, or outlet. Take a poo, in a jar and keep it. Sealed. Bring it out just before you place is about to be shown. Hide it in a vent. When people catch a whiff claim this is a problem that comes and goes and that you have cntacted the city and been told that has to do with the sewer system. Golden. Be sure to remove the turd jar as soon as they are gone, unless of course you like the smell.
*Can really be used nowadays to describe anyone you think is lame and has more money than you.