Last time I recieved a series of marketing messages over SMS, they implied I'd opted in, and included links to opt out. This went on for a year. Not often, about once a week, varying.

I thought I must have "opted in" non-consensually on some website (dark patterns abound), but I couldn't figure out which one. After a while I decided they were spam and it was best to not click the product links or opt-outs. Same reason we were taught to not click the opt-out links in spam email: Telling them a real person is reading increases your address's value as a target..

It took over a year before I spotted on my mobile bill that these were incoming premium rate SMS. This is in the UK, where incoming SMS is normally free, but each of these messages added a few £ to the mobile bill. They weren't spam, they were designed to look like spam! So the recipient would just ignore them if they were infrequent. They took about £100 total.

When I spoke with the mobile service provider, they said I must have agreed to receive them and I should contact the sender. As if I could figure out who they were and as if scammers would care. Later the provider said it was a known, common form of fraud but sorry, they couldn't block it or compensate.

Needless to say, I'm wary of incoming SMS that seems like marketing now. Even a message asking if I'd like to opt in would have me checking my next bill to see if it was SMS fraud, unless I recognised the connection to somewhere I agreed to receive messages from.