The next time you get a knock on the door, think twice before you open up. That's the warning from the Better Business Bureau about door-to-door scams.

A knock at the door recently interrupted Gretchen Kennedy while she was working from home. When she opened it, she saw two young men on her porch.

"They said that they were selling magazines and I said I wasn't interested. I declined several times," Kennedy said.

She finally caved in because they said it would help charter schools, but the magazine never arrived. When she complained, the company never responded.

"It angers me that, that someone would do, pull the fundraising card," she said. 

Kennedy fell victim to one of the latest door-to-door sales scams out there.

"They will normally try to pull at your heart strings, pull at your purse strings," said Carrie Hurt with the Better Business Bureau.

Our investigation reveals the number of complaints the Better Business Bureau received about door-to-door sales more than doubled from 600 in 2010 to 1,300 in 2011.

So far in 2012, it's up again.

Complaints from consumers who say they never got what they paid for and were victims of aggressive sellers using high pressure tactics.

"They will use something like, you know, using the safety of your family, your home isn't safe," Hurt said.

Ironic, since our crime and safety analyst said what's really unsafe is letting a stranger in the door in the first place.

"Cause you've got some people posing as salespeople and they will watch and see who lives there and while they're at the door, they're looking around to see if there's something in there they may want to come back to get. You never know who's on the other side of that door," Channel 4 crime expert Ken Jefferson said.

Former door to door salesman Elliott Shouse said they're trained to get you to let them in. Once they do, he claims they're told to scare you. Shouse took a job selling windows door to door. He said he quit after the first day.

Shouse said this is what they suggested, "Go into the kids rooms and if the windows didn't open to tell the people that their kids would die if they didn't buy these products."

That's why Jefferson said "if" you let someone in your home and they put on the pressure, you need to realize it's likely a scam. Ask them to leave, and if they don't call the police.

"Scammers will knock on your door too and they're slick tongued, fast talkers and before you have a chance to know what they're saying, they already have you going to the bank getting money out of your account," Jefferson said. "Or you pay them to do work and they don't finish the job. Rule of thumb is don't answer the door."

So what are the newest door-to-door products racking up complaints?
Security systems, produce and meats, cosmetics, cleaning supplies, photography sales and magazines.

We found the company Kennedy paid has an "F" rating with the BBB and more than 170 complaints.

"I was angry that I was duped," Kennedy said.