MTurk – THE MECHANICAL TURK – mturk.com – an Amazon subsidiary.
This site gives the widest range of tasks, but if you want to make serious money you need to be from the US. There are people from other countries that can get cash payments ( India and some non-public schemes in Africa), but the UK is not one of them, and that is where my interest ends. I have found web comments that indicate they are not paying cash to new Indian workers.
They can accept workers from any nation, but it is hard for non-US people to get accepted these days, and the only way to get rewards is to put that money into a US Amazon account as a gift card which can only be used to buy products on US Amazon.
Be aware that you are not allowed to start working on HITs until you have gone through an “interview” about income tax – even if you’re not a US citizen. You may be allowed to browse through the HITs, but DO NOT attempt any.
If you are in the US, it should be your first choice for regular crowdsourcing work, especially if you have good writing skills and typing speed.
If you are not in the US, be aware that the high-paying jobs mostly expect American grammar and syntax. On one occasion, I got an external assessor report (for a $5 job) doubting that English was my first language! Since the assessor’s report had a couple of spelling mistakes and a grammatical error, I avoided more HITs from that originator.
If you want to work to buy something, and it can be bought on Amazon USA, MTurk can still be useful to acceptable non-US citizens who cannot get paid in cash.
If you really know what is worthwhile about certain items being bargains on Amazon, you can do the HIT work and list those items on eBay – when you get an eBay sale, you buy the item on Amazon and have it shipped directly to the purchaser as a gift (so that an invoice is not included). If the purchaser asks, you say that you use the Fulfilment By Amazon service.
That really is a black art, because you have to buy from Amazon USA. To avoid customs charges you need to pick items that cost less than $15/£15, and to minimise the costs of sale on eBay you want to be as close as possible to that $15/£15 sale price. There is also the potential difficulty of the item being out of stock when you get to Amazon to buy it. Whatever, some people do it … perhaps they are listing items on US eBay.