I have a lot of respect for PigletJohn who posted upthread. He is the MN resident expert Plumber so knows his tradesmen and he says this is just testing to see if you're a pushover. As he says, give tradesmen free access to the kitchen and say 'help yourself' and they really will. He knows the reality.
Interested too in the American perspective and that workmen there never would expect to be given drinks or food and expect to bring their own. Of course, most other people working out if the office or away from home in the UK expect to provide their own too. Mobile hairdressers might be given a drink but probably wouldn't ask for lunch and similar for the piano tuner, the tutor who comes to teach children, a financial adviser who visits at home, the salesman showing carpet samples etc etc. People expect to bring their own and take a short break away from the client, having a breather and eating their lunch or to head to a cafe or shop to grab a sandwich. They provided for themselves.
This idea of hourly coffee and an endless supply of biscuits being a good thing or needed to get the job done seems peculiarly British. And lots of people on this thread are clearly big supporters of it....do they feel their hospitality is somehow on show or its some kind of community activity? Perhaps it goes back to when tradesmen were locals and usually known to you - so you would feed and water these people who were your neighbours and friends....but things are different now, but somehow people haven't move on in their expectations.
In what other industry is it okay to have a break after 30 mins of work or to stop for multiple breaks during the day, whisky being paid....and to look a bit disgruntled in certain types of biscuits are offered? Is this a thing about male workmen and their interactions with historically women who are housewives? I'm really interested in where this actually quite unusual social dynamic between workmen and women who are employing them comes from and why so many people are positively effusive about cooking up bacon rolls and offering significant hospitality for them.
I say again, if you choose to offer..I find it a bit interesting and surprising, but no problem becaue it's your choice to do so. Very different from expecting and asking...I think it's probably quite manipulative and as PigletJohn says, a way of sizing people up....not just for if they're kind or hospitable, but also whether they might be taken advantage of in terms of pricing, reliability etc. It's overstepping the mark. Like Op lots of people say they would have been caught off guard......in itself, the behaviour is appropriate because it intends to catch someone off guard.