@Mati_and_Karolina When writing about sitters, you wrote:
“That is often very hard work which is paid only by thank you and happiness of pets.”
Um, that is incorrect. House sitters receive free lodging.
And in exchange, homeowners get someone to provide free pet/house sitting.
We are HOs and sitters and we believe it is a mutually beneficial exchange. So we do see it from both sides. 
Hi all. I believe there are more vapers than smokers nowadays as seen as a safer option. As a vaper I would never vape in someones home but would go outside. I like a glass of wine but would never over indulge whilst caring for pets. (If a pet was taken ill a taxi can be taken to vets) I personally would not accept a sit if no vaping outside and no alcohol was stated. If you smelt smoke indoors really think it was from a cigarette not vaping. As you said the sitters did a great job, surely this is the important factor. As others have said, make it clear from the outset but believe your pool of sitters would be reduced if no alcohol or vaping outside was stated.
I agree with most other commenters here- smoking & vaping inside is a no go. As an HO I would specify a preferance for complete non smokers because even if people smoke outside they still bring the smell in on their clothes & breath. I am an ex smoker so speak from experience!
As a sitter I would not apply for, or accept, a sit where alcohol was banned. I am a social drinker, not an alcoholic, and (moderate) drinking is accepted pretty much everywhere so I’d find that overly restrictive. I also don’t apply for sits specifying Vegan/Vegetarian only - because I do eat some meat and I would not want to go against the owners wishes. I also don’t apply for sits where there are more pets than i’d wish to handle or where there is too much workload- so the exchange does not feel equal- or where the dogs can’t be left long or need to much attention. Etc etc…In the end it boils down to finding a good match between sitter and host. Its just a matter of time- the more restrictions the longer it might take but I do believe that every sitter and every host can eventually find their perfect match! 
Greetings!
I would definitely write down something I wouldn’t want any sitter to do in your home.
That said, I myself am a housesitter from a recreational state who really needs their Green Medicine (Cannabis/Marijuana) to function.
If they need to smoke, you can have them do it outside and put any butts in the trash.
@KenandMary1998 Um, the statement is 100% correct. Sitters/Guests on this site are not paid. Payment is not exchange. The IRS is not going to expect a W2 or 1099 for what is meant to be equitable exchange. A paid Petsitter who would be hired for an overnight sit would receive monetary compensation AND a place to stay. You may prefer to view the your home or others as a form of payment, but legally, it is not.
It would never occur to me to ask whether it was okay for me to drink wine on a sit. It would also never occur to me to smoke anything indoors on a sit. To me (midwestern American) those seem like two completely different questions.