It's impossible to tell if the home is/was occupied by smokers without actually asking the homeowner's themselves. If you smell the remnants of smoke though, it's likely there are smokers living in the home. If you really love the house, as mentioned by Bill, there are ways to get rid of the odors. If it's a major problem for you, you could ask the owner's to do the clean-up before you make your offer. If it's something you are willing to do on your own, ask that the expense be taken off from the price of the home. If they say they are not smokers, the smell/odors could be coming from somewhere else, and you want to find that source!
Cigarette smoke odors are primarily absorbed into walls and floors (especially carpeting). These are the two areas to attack first. Try washing the walls, if possible, first. If that doesn't work you'll have to repaint, but use a sealant to make sure you're covering up those odors for good! Then, if the home is carpeted, get it shampooed and/or cleaned professionally. The use of ammonia and vinegar are also helpful in removing the odors from other places such as counters and appliances. Setting out bowls of ammonia or vinegar may help to remove the smell from the air as well.
I wish you luck!
[Shannon] of DesigningReality - Home Staging, Real Estate Photography, and Design in New York and New Jersey.
If you like the home, consider building this expense into your offer and consider it a non-issue.
Focus on identifying the right home, in the right location, offered at the right price.
The "Eckler Team"