Could anyone mention good and bad software for bicycle inventory and rentals, and explain why? Also, anyone who has a bicycle rental business, could say what are the biggest problems regarding the management?

No.. Trade secrets and other stuff. I could write you one but you would have to pay me money. Otherwise it has to be scrum agile, docker and cloud based.. preferably not using azure. Hadoop could be good but you need ITL6 for load balancing and compiled Java. I'll just get back to lacing a wheel. Much more therapeutic.

Small companies generally have to use a software product that is adaptive to a wide range of accounting, billing practices, product and inventory control. That means an off the shelf product. Even so, then costs are high. But more custom products require even more money as the uniqueness makes them have less sales potential in the market.

So I'd say you'll have to look at things like Quickbooks and such. To use them effectively you have to really understand what your processes are and how they work together. The way off the shelf software requires you to set it up has a lot of adminstrative overhead.

A friend I worked for was always having to deal with inventory issues and job costing issues with his software. Both quickbooks and system for job labor and materials handling. So much time, that I wondered if it was worth using a computer for such a small company. I spent as much time verifying the errors manually as I would have just doing the tracking on paper.

I would think the best approach would be to Google bicycle rental software and then check user reviews and ratings. That would be a much more focused effort, and at the same time would entail a wider sample of users.