I am sure there is a catch-like a 2 year contract. No one gives you a phone for $1

If your searching for a phone that takes a sim card for like a GSM phone try going to www.ever buying.net and look for a phablet or phone they have cool phones at a much better price keep in mind the shipping can take up to 25 days depending on what method you check. As far as from best buy I don't know what the conversion is so I would say yes if you have to ask its to good to be true. Now you could also check out www.aliexpress.com also.

A Samsung Galaxy S5 today 4/172016 Should cost $300.00 US, (refurbished), or $399-$450 US dollars (NEW), If you buy one cheaper, it is not a real Samsung phone.

In my area, no cost phones generally require you commit to a 3 year contract, so in fact you are paying for the phone. Do your best not to get roped into that long of a contract. From my own experience, contracts leave you vulnerable to unreasonable extra charges and cost increases throughout and since you are on contract you give up all bargaining power.

Best place to buy unlocked phones is E-Bay. But again, you have to know what you're buying and will it work for you and the carriers in your area. Now there are a lot of companies where you can actually just pay for the phone and get phone service for free - just don't get greedy or you will wind up paying for service too. Best in the USA is Freedom. Pop. If you want the latest phones (with ALL the bells and whistles) at the best prices, then you can't beat AliExpress. They don't have the "cheapest" prices because they take a cut, but if you buy from some of the other Chinese companies you will pay and never see your products.
As for the £1 phone - only with a contract for at least 2 years.

There will never be such deal that is legitimate. For sure it has a catch or maybe the seller hasn't thought of a final price or it is still negotiable.