My local co-op, of which I like to play unofficial volunteer at, just fixes donations up as is to make them good riders, but stops at that. When people come in if they see something they like, but wish it was slightly different, well that's what the hourly stand time is for and we'll help them make it what they desire, even if it wouldn't be our recommendation. The only things we really push back on are modifications that may be dangerous. Inconvenient? Nah, they'll learn, they'll be back Just the fact someone is interested in bikes prompts me to give blanket enthusiasm first and foremost.