At McDonald's you're asked 'do you want fries with that?'.  With rental cars they're sorry but there are no small cars currently available but for an extra $12 a day you can be upgraded to a midsize.

These are just examples of upselling to increase the average sale per customer.  The purpose is to sell as many add-ons as possible, whether or not it's in your best interest to buy them.  And that is what is wrong with upselling as a strategy!

For everyone in sales, especially those being asked for advice, it can be a way to lose the sale and the customer.

You must keep the best interest of the customer in mind, so:

1. Help them figure out what their problem is.

Even if they're ready to buy, help them clarify and pinpoint the problem.  It also builds trust and demonstrates your knowledge.

2. Point them in the right direction, even if that direction is not you this time.

You wouldn't sell a friend a service he didn't need, so the same rule applies here.  That is, don't sell something, especially upgraded or gold-plated, if it is not what's needed.  If you do, you won't develop a reputation as a trusted and knowledgeable expert.

Selling isn't about convincing people or taking advantage of them.  It's really about matching - clearly defining the problem and then finding the right solution.  Hopefully, you will be that right solution, but even if you're not this time, the customer will remember you did the right thing and be willing to trust you in the future.