The smallest client I have had was the length of my thumb-- probably about 2 inches I guess. I was so shocked, I had never seen one that small.
He had booked for 2 hours so it was awkward because he expected penetration and was paying quite a bit, and it didn't occur to me at the time that the condom slipping off would be a huge danger. When I look back on it I should have just refused, but I said OK-- I had to get on top of him for it to work, or doggy. When he came the condom did slip off but it was stuck to the walls of my vagina so I had to just pull it out from inside me so I was fine, but after that experience I will never have penetration with someone who's so small the condom doesn't fit.
You can give them OWO, I find that the smaller a penis is the the better oral I can give as I have more space in my mouth to be creative with me tongue and whatnot.