It said it was hearing of more cases of horses being sold-on for profit or sent to abattoirs.
The caution from NED follows the same case cited by World Horse Welfare - that of 24-year-old Brooke Lee, of Roebuck Lane, Otley.
City of York Council's Animal Health Service began its inquiries into the case in 2010.
Earlier this month, Lee was sentenced in the Crown Court after last year pleading guilty to two offences of fraud, and one of trading without professional diligence (trading unfairly).
Lee sold a horse for £1837.50 at a local livestock market as "good to do in every way", but she knew the horse was lame.
Officers contacted the previous owners who were shocked to hear that the horse had been sold. They had given the horse to Lee just five days earlier on the understanding that the horse would have a permanent home as a companion for her filly.
Officers then began investigating other horses that Lee had acquired.
A pattern emerged and a further four horse owners told officers that Lee, using different names, had tricked them into letting her take their horse, believing it would be given a permanent home.
In one case the horse was taken to market a few days later where it was sold for £480 and slaughtered. Lee continued to misinform the previous owner saying that she still had the horse with her in the field.
Trading Standards Manager at City of York Council, Matt Boxall, said: "Miss Lee tricked people into giving her their retired horses - which at their stage in life, needed to take things easy.
"The lies she told led the owners to believe they were doing the right thing for their animals, that they would be loved and cared for forever.
"Instead, they were simply sold on to unsuspecting customers. All of the complainants have described their devastation upon finding out their horses had been treated this way".
Lee was sentenced to nine months imprisonment, suspended for two years, and was ordered to do 220 hours of unpaid work. She was also ordered to pay £750 in prosecution costs.
A similar case involving deceiving horse owners has also been before the courts in the United States.
NED said that before people loaned their horse to a stranger, or even to someone they knew well, they should take a few sensible precautions.
The UK HorseWatch Alliance, in association with NED, has put together a checklist which can be viewed here.
NED said a BBC consumer affairs series, "The Legalizer" is looking for people to take part in a new series which aims to show consumers how they can uphold their rights, through the courts if necessary.
It is presented by a barrister who will use his knowledge of the justice system to show citizens that they are not helpless and can use the law to resolve things for themselves.
The series will look into individual cases and explain to viewers how the Small Claims Court process works and how to use it.
Fulcrum TV, the producers, are looking for people having problems recovering horses that have disappeared whilst on loan or are trying to seek financial recompense for a horse going missing or being sold without the knowledge of the owner.
More information: www.nedonline.co.uk