I only flip offroad bikes and atvs, sold as-is where-is no warranty. I look for flashy bikes with bolt on parts and destroyed engine internals. Or even better, when all the parts are present, but in tupperware and baggies. Those are fun for me, I like that puzzle.
My best flip to date was a filthy KX80 I bought for $300, power washed it and put back on kijiji. Sold it a couple days later still broken but clean for $600.
Missed breaking even by $7 on a bike I bought for $100. Another machine I ended up losing $50 when a weak battery let me down. Guy showed up with cash, wouldnt start, guy wanted $50 off previous offer to offset a new battery, I wanted to stop the bleeding haha.