Easy solution to keep the carpets clean

We had carpets shampooed and (naturally) wanted to keep them clean for as long as we showed the property. I was suggested to buy a roll of sticky film from HomeDepot ($10 that only covered 20 steps and 1 room). I rolled it on the steps and in the bedroom and had it removed the same evening (good bye $10) - first of all, it'll take 3-4 rolls to have all carpets covered in the townhome ($40). Second of all - it didn't stick flat, most of it was lumpy and I didn't want anyone to slip when going down the stairs.

Solution? I plainly asked prospective tenants to remove the shoes. Some of them even had them removed the moment they walked in before I asked for it (I took off mine and placed them in the foyer where everyone can see). Nobody refused or objected. And if they would, it'd tell me something about them, wouldn't it? 

Why buy expensive film which you can use only once, if you can ask the prospective tenants to take the shoes off.