...and yet people buy stuff from grow shops all the time and never get busted. Being paranoid is OK in small doses. Anything more and you're just frying your nerves for no good reason. That said, you could try to drive by the business at different times of the day and try to stop in when there are no or few other cars parked there - my local shop is barren the first 2 hours other than people quickly coming in, grabbing something and leaving. Walk in, quickly scan around for suspicious cop types. Clear? Grab one of the dudes that works there ASAP, be prepared and tell them exactly what you want. Get your stuff, pay and GTFO. Less time there = less risk.
I would even call ahead to check if they have what you need - if they're nice like my guys they'll pull everything for you so it's sitting by the front register ready to rock.
No offense neno, but I don't think you've ever been in a hydro shop - the people are cool, never ask your name or get into your business and probably could give a shit as long as you're not annoying them. Unless you live in cali or a major metro area they're probably not very busy most of the time.
Seriously, unless you say some stupid shit like HAY CAN I HAZ SUM LITES 2 GROW IZ DIZ ONE GUD FER MARIJUANA? you will have ZERO problems with a hydro store. I'd rather hit up the local hydro store than have it shipped from an online place that might slap HYDROPONICS GROW LIGHTS all over packages and then have it show up when I'm not home and sit on my doorstep for half a day incriminating the shit out of me.