This industry just has a different culture, I guess. I personally haven't mailed any gifts to any schedulers, project managers, etc., as I haven't made a significant amount in a company to justify any gifts hahaha; however, I have received a nice Starbucks gift card or two from select companies from their project managers for some of the long-term projects I worked with them.
In my full-time career as a pipeline engineer, I work with many other parties in my projects, with many working from home at their home offices. Around Christmas time, that's when the nice and thoughtful gifts come in, with my favorite being those boxes of Dietsch Brothers chocolate covered pretzels from a consultant I worked with in years ago!
To loop back to the main topic with the world of mystery shopping, I personally wouldn't be offended if I received gifts from those that made me a significant amount of money throughout the year, with my recent experience from receiving even just a 'thank you' card with a $10 Starbucks gift card, which more than enough and I appreciated very much.
Shopping the Greater Denver Area, Colorado Springs and in-between in Colorado. 33 year old male and willing to travel!