If you bid on terms related to flowers, and you sell flowers, then yes - you'll get high quality visitors. If you bid on terms related to flowers, but you sell car repair services, then no - you'll just get random page hits.
If they're keyword targeted ads on google's search pages, then as others have said, it's in your control to select your keywords, and word your ad, to get the sort of visitors you want. As far as content network ads go, the adsense ads that appear on webpages, they can be more random if you don't keep a check. In the first instance you can check where your clicks are coming from, and if it's not the sort of sites you want, you place those sites on your excluded list; and then also run a placement report, and see if there are more sites that your ads are appearing on that you want to exclude.