I asked the landlord after I had signed the lease agreement (so they couldn't deny us the house, ha ha!). I don't like being dishonest with people, and was really worried that the landlord would find out I had snakes and kick me and my housemates out, which is why I asked. I figured I could keep a click-clack hidden (I was getting a hatchie, no matter what!), but would have trouble hiding an adult carpet.
Fortunately I was allowed =) so now I'm working on a kick-a$$ enclosure for display!!
The reason landlords say "no pets" is to prevent damage (scratches, stains, etc) to their property, which is understandable. However, if you kept an animal that is in a confined area (e.g. rep in tank), is never let out without supervision, and can't really cause damage to the house, there should be much of a problem.
If you ask your landlord to keep reptiles, emphasise this fact, promise to lock all cages (not a bad idea regardless), and offer to talk about any other conditions they may have. With a lizard there might be a slight risk of scratches to the floor, but this is easily combated by putting a rug on the floor, or letting the animal play outside.
Good luck with the real estate agent and landlord, I hope you're allowed to keep reps. Look at it this way; if you don't ask, you'll be hiding the animals, right? If you ask and they say yes, woo! No problem! If they say no, you'll be hiding them like you originally intended, so it doesn't hurt to ask. Good luck!