It is most likely to be under the Theft Act, which needs prove of dishonesty. The wording in this offence basically states 'the accused must know or believe that the goods are stolen at the time of the alleged handling. This is fairly difficult to prove, particularly in the situation as you have described, i.e., individual online purchases where prices could be much lower than the expected market value due to the nature of bidding.
If the police can not prove you had actual knowledge (knew) that the property was stolen then they have to look at your 'belief', and one way to consider this is the market value of the property the accused paid for it.
Here is a bit of stated Case Law-
·A person knows that goods are stolen if he has actual knowledge of this, or if he is told of this by someone with first-hand knowledge (eg, by the thief himself). 'Belief' was something short of knowledge, and applied to the situation where the person could not say for certain that the goods were stolen, but there was no other reasonable conclusion in the light of all the circumstances.
Did the police disclose any evidence in interview, or to your solicitor to suggest you must have known or believed the property to be stolen or was it obvious you had been arrested solely because of of an investigation into stolen phones later showed you were in possession at a later date?.
Obviously, I can not say what will happen when you return on bail but highlighting the difficulties the prosecution side face when investigating this offence.
The fact that you have no pre-cons for any theft offences is relevant in this case.