My case:
I worked out how much I was spending on PAYG valeting and realised for a little more, I could employ someone 2 or 3 days per week for not much more. So I have and my business has revolutionalised.
He moves stock, handles customers (when I am busy), test drives, collects cars, parts, valets, answers the phone, fits number plates, small non-skilled mechanical fixes, inflates tyres - you get the picture.
Costs me £9 per hour and he is now more or less full time, all above board with invoice plus he invoices other work on the days off, so I am covered from the 13 week employment law.
Yes, we have run ins and I have lost my shit twice with him (speed and talking too much on his phone) but he is great to have around.
Conclusion: I couldn't manage the level I am at (around 15-20 stock) without him now (or someone else if he goes).