Editor's note: Inc.com columnist Alison Green answers questions about workplace and management issues -- everything from how to deal with a micromanaging boss to how to talk to someone on your team about body odor.

A reader writes:

I'm in a job I really enjoy, but as part of my role, the admin assistant puts through quite a lot of cold calls to me (which always turn out to be advertising calls, but disguised as other things which is why they get put through in the first place!). Usually they're from telephone companies or software companies who want to sell new products or upgraded service. At home, I have a variety of tried-and-true techniques for dealing with these people (the most successful one being Caller ID and just not answering my phone to unknown callers - fortunately that's possible for me!) - but in an office environment, that's not really possible. And while I'd like to think I'm respectful to everyone who calls me, it's a bit frustrating to deal with a salesperson who won't take "No, we're not interested in that product, thank you" for an answer when simply hanging up the phone isn't an option like it is at home.

Usually I crack under the pressure and end up "agreeing" for them to "check back in a while," which is definitely wrong for everyone.

I'm hoping for a professional and polite way to shut down these conversations before they start and stop giving them excuses to call back - and what the etiquette generally is on this. Strategies I've tried so far:

1. Saying I'm not the person who can make those decisions (which, while half-true, just compounds the problem since they then ask who does deal with it).

2. Saying we have our own supplier purchasing arrangements and we are fine with those (which just leads them into a dialogue about what a good deal they're offering and how we'd be crazy not to seriously consider their offer).

3. Agreeing to "think about it" (the worst of all things to say, since it gets them off the phone but guarantees a call back).

Please, please help!

First and foremost, you need to get comfortable with the idea that you get to decide how much time you spend on the call with salespeople -- not them. That means being more assertive and not afraid to just cut people off and end the call. You can do that by saying politely that you're not interested once, and then saying it again and hanging up if they persist.

For example:

Caller: I'd like to talk to you about your paper supplier. We have some great deals I think you'd be interested in.
You: No, thank you, we're very happy with our current supplier and aren't interested in switching.
Caller: Give me just a few minutes; I think you'll want to hear about the special we're running this month.
You: No, thank you. Would you please remove us from your list? I appreciate it. Goodbye. (hang up)

Or here's another version:

Caller: I'd like to talk to you about your paper supplier. We have some great deals I think you'd be interested in.
You: We don't accept unsolicited sales calls, but you're welcome to put the information in the mail.
Caller: Give me just a few minutes of your time; I think you'll want to hear about the special we're running this month.
You: No, thank you. Have a good day. Goodbye. (hang up)

You also don't need to get drawn into long interrogations when you know it's a sales call that you're not interested in. For instance, if you get a caller who starts asking you obviously sales-oriented questions rather than giving you a direct sales pitch, you can redirect the conversation like this:

Caller: Who do you currently buy your toner from?
You: We're happy with our current vendor. Would you please remove our number from your list?
Caller: Aren't you interested in saving money on a better deal?
You: We're happy with our current vendor. Please remove our number from your list. Have a good day. (hang up)

The point here is that you're not at their mercy, stuck talking to them until they agree to end the conversation. You can control what questions you do and don't answer, how much time you spend on the call, and when it ends.

Yes, of course it's rude to just hang up on someone as soon as you realize it's a sales call, but you can give them one opportunity to end the call politely, and if they ignore you, you can assert your right to manage your own time by politely ending the conversation yourself.

Now, obviously, if you work for an employer who has directed you to talk to salespeople for as long as the salesperson wants and never to initiate the end of a call with a salesperson, this advice won't apply. But I doubt that's the case. Usually what employers want is for you to be polite to callers but assertive about controlling your time. In fact, I've been concerned plenty of times about people spending too long on these calls (out of a desire to be polite), but have never once thought, "Oh, she should have let them finish their sales pitch." If you have any doubt about this, you can check with your boss -- but this is almost certainly what you'll find.

Be polite, but quickly explain you're not interested and end the call -- whether they're on board with ending it or not.

Want to submit a question of your own? Send it to alison@askamanager.org.