First things first: know who handles product presentations and continuing ed seminars in your office. If you're in a small office, that might mean you (or whoever's being asked by the vendor). As someone who handled every aspect of seminar coordination for ten months, I highly recommend that the scheduling, lunch deliveries, and presenter setup (e.g., if they need an LCD projector for a PowerPoint presentation) be handled by an administrative assistant or office manager, but the yea-or-nay on having the presentation in the first place be decided by an architect. (Trust me--even as an intern, you don't have time to do your actual architectural job plus field all the phone calls and coordinate seminars.) Ask the vendor if they have any AIA-approved continuing ed seminars. Even if your colleagues aren't AIA members, some states still require continuing education credits in order to maintain licensure, and these presentation can be a good way to get those credits as well as learn something that really helps you in your day-to-day jobs.
Second, check with your boss or firm principals if you're unsure about accepting a lunch invitation or an activity invitation from a product rep. In particular, ask him/her how much, if any, project information you're allowed to share. Bear in mind that part of taking you to lunch is sometimes to find out about possible leads, so they may want to know if the Thus-n-Such Elite Condo project is about to go out to bid or if it's still in DDs, and can they get their products in the project or help you with the specs?* If a vendor asks about a project, you may be able to at least say when construction is slated to begin and who is handling product inquiries. (For example, I do a lot of healthcare work with health systems and HMO companies that have contracts with various product and equipment vendors. In those cases, I tell vendors, "Those decisions are made at a national level--I have no influence over whose storage cabinets or autoclaves they use. If you want to get on their list, talk to X person in Minnesota.")
There are ethical rules in place that keep architects from buying work from a client by donating to that client's organization or favorite charity. Your firm principal(s) may have similar rules about accepting gifts, lunches, dinner/drinks, or golfing or skiing outings from vendors and potential consultants as well. Ask first just to be safe. Also, let your manager know if and when you'll be meeting with product reps regarding a specific project. Chances are, your manager has had experiences with similar products and materials and will have questions that they'll want to ask of that rep themselves (or want you to ask on their behalf). It's a good way to learn about the kinds of information you really need from product reps as well as gain a better understanding of how materials work in a building.
Bad product reps call you and leave a voicemail, then email you ten minutes later to see if you got the message, then show up unannounced at your office to see you two hours later (and yes, this actually happened to me recently). Good product reps, however, are much more than salespeople--they understand the forces and issues that affect their product and how it works in your building. Sometimes they were architects, engineers, nurses, teachers, etc. before they were reps, so they can bring an extra layer of knowledge to your project and product selection. This is why bringing some product reps in as early as possible into a project--during early DDs, for example--can be important. You can (hopefully) get the right knowledge and the right product for the job. Some of the best reps I've ever worked with have flat-out told me when their product was not the right one for the job. It made me want to use them again on another project as soon as I could. And frankly, there are a couple that I've worked with for so long that I actually hang out with them socially, just for the fun of it.
*Many product reps will help you in part or in whole with certain spec sections to make sure that their product--or at least one that works as well as theirs--is in your project, thereby assuring a certain level of quality. This happens a lot with door hardware, where the consultant who assembles and assigns hardware groups to your doors will also write the spec to make sure certain products (or at least products of a certain quality) are specified. I've also seen this happen with concrete mixes and admixtures, thermal insulation and waterproofing, and lighting.
If you have a question or a topic you'd like to see discussed here, let me know in the comments or drop me a line via email in the sidebar. Thanks!